Here's an acoustic tab done based off of the live performance on her channel by ear. 
https://www.youtube.com/watch?v=CFsuQVB1Hyo 
 
I don't know the exact accurate chords he uses but these are what I've used for a decent beginner cover. 
Here's my version for reference 
https://www.youtube.com/watch?v=JBHTJDeGcvQ 
 
The timing from the ultimate-guitar player is a little off but if you use the tabs in accordance with the actual
track you should be perfectly fine.
------------------------------------------------------------------------------- 
                             MUST BE LOVE - Christina Grimmie 
------------------------------------------------------------------------------- 
Tabbed by: JustSleightly 
 
Tuning: Standard 
 
************************************ 
 
| /   slide up 
| \   slide down 
| h   hammer-on 
| p   pull-off 
| ~   vibrato 
| +   harmonic 
| x   Mute note 
| b   Bend 
| pb  Pre-bend 
| br  Bend release 
| pbr Pre-bend release 
| brb Bend release bend 
 
************************************ 
 
Intro:
e|-------------------------------------------|----------------------------------------------|
B|-------------------------------------------|----------------------------------------------|
G|-------------------------------------------|----------------------------------------------|
D|-------------------------------------------|----------------------------------------------|
A|-0-0---5/7---0-0--5/7---0-0--5/7-----------|--0-0---5/7---0-0--5/7---0-0--5/7--7-777-x----|
E|-------------------------------------------|----------------------------------------------|
 
Verse 1:
e|-------------------------------------------|   |----------------------------------------------|
B|-------------------------------------------|   |----------------------------------------------|
G|-------------------------------------------|   |----------------------------------------------|
D|-------------------------------------------|x3 |----------------------------------------------|
A|-0-0---5/7---0-0--5/7---0-0--5/7--7-777-7--|   |--0-0---5/7---0-0--5/7------------------------|
E|-------------------------------------------|   |-------------------------5\0------------------|
 
I was sitting at the mall with my friends on a Monday 
Saying I was gonna leave this town 
This town, run away 
But then you walked in and I think my heart don't skip a beat 
One look and everything just froze 
 
e|-------------------------------------------|   |----------------------------------------------|
B|-------------------------------------------|   |----------------------------------------------|
G|-------------------------------------------|   |----------------------------------------------|
D|-------------------------------------------|x3 |----------------------------------------------|
A|-0-0---5/7---0-0--5/7---0-0--5/7--7-777-7--|   |--0-0---5/7---0-0--5/7------------------------|
E|-------------------------------------------|   |-------------------------5\0------------------|
 
Like a rock rolling down a hill 
Like a car with no one at the wheel 
Take me to a doctor cause I'm shaking 
I need water tell me do they have a pill 
I'm feeling ill 
 
Chorus: 
           Am               Am 
It must be love, it must be love 
           F        G       Am 
It must be loooooooooooooooooove, 
           Am               Am 
it must be love, It must be love 
           F        G       Am 
It must be loooooooooooooooooove 
           Am               Am 
It's in my heart, it's in my body 
           F        G       Am 
It must be loooooooooooooooooove 
 
Verse 2: (Same as Verse 1 but the first half ends slightly differently)
e|-------------------------------------------|   |----------------------------------------------|
B|-------------------------------------------|   |----------------------------------------------|
G|-------------------------------------------|   |----------------------------------------------|
D|-------------------------------------------|x3 |----------------------------------------------|
A|-0-0---5/7---0-0--5/7---0-0--5/7--7-777-7--|   |--0-0---5/7---0-0--5/7------------------------|
E|-------------------------------------------|   |-------------------------5\0----0-1-0-0-0-----|
 
I'm working not to say this and mind my own business 
Ain't looking for trouble, got no man as part of my wishlist 
But now you're in my head 
Get outta there get here instead 
One smile and everything just froze 
 
e|-------------------------------------------|   |----------------------------------------------|
B|-------------------------------------------|   |----------------------------------------------|
G|-------------------------------------------|   |----------------------------------------------|
D|-------------------------------------------|x3 |----------------------------------------------|
A|-0-0---5/7---0-0--5/7---0-0--5/7--7-777-7--|   |--0-0---5/7---0-0--5/7------------------------|
E|-------------------------------------------|   |-------------------------5\0------------------|
 
Like a rock rolling down a hill 
Like a car with no one at the wheel 
Take me to a doctor cause I'm shaking 
I need water tell me do they have a pill 
I'm feeling ill 
 
Chorus: 
           Am               Am 
It must be love, it must be love 
           F        G       Am 
It must be loooooooooooooooooove, 
           Am               Am 
it must be love, It must be love 
           F        G       Am 
It must be loooooooooooooooooove 
           Am               Am 
It's in my heart, it's in my body 
           F        G       Am 
It must be loooooooooooooooooove 
 
Bridge: 
Break/Acoustic Percussion solo (See included videos above for this portion) 
 
Doctor beat my chest 
Get out of my bones 
Not baby for this 
What's fun on my own 
Clashes in my head and there must be something wrong 
I don't know what you did 
But I can't leave you alone 
 
Outro:
e|-------------------------------------------|
B|-------------------------------------------|
G|-------7/9--------7/9--------7/9--9-999-9--|
D|-7-7--------7-7---------7-7----------------|x2
A|-------------------------------------------|
E|-------------------------------------------|
 
e|-------------------------------------------|   |----------------------------------------------|
B|-------------------------------------------|   |----------------------------------------------|
G|-------------------------------------------|   |----------------------------------------------|
D|-------------------------------------------|   |----------------------------------------------|
A|-0-0---5/7---0-0--5/7---0-0--5/7--7-777-7--|   |--0-0---5/7---0-0--5/7------------------------|
E|-------------------------------------------|   |-------------------------5\0------------------|
 
Chorus: 
           Am               Am 
It must be love, it must be love 
           F        G       Am 
It must be loooooooooooooooooove, 
           Am               Am 
it must be love, It must be love 
           F        G       Am 
It must be loooooooooooooooooove 
           Am               Am 
It's in my heart, it's in my body 
           F        G       Am