IMPORTANT: I transcribed this for the piano. So this is the piano notes. I was not
sure what to label this as, type-wise. However I am sure it would work for guitar. I do
by ear, but this is what she is playing, I am fairly certain. i just thought that since 
love this song and it is fun to play, others would like to play it too! Hope this helps. :)

Throughout the entire song she is playing this:

F# C#-D#-C# C#-D#-C# G# C#-D#-C# A# C#-F-C#

This means that the base notes are F#, G#, and A#. You play one base note in your left
and with your right hand you play the C#-D#-C# bit quickly (I would say sixteenth notes,
I play and sing simultaneously, so it's really just whatever fits the song). Listen to 
song to get the rhythm.

Midway through the song, you move your left hand down an octave. at one point in one of
recordings, Regina plays a C-natural instead of C# in the song, but quickly starts doing
C# again. So I think that was a mistake. Because in other recordings of this song she 
not do that.

It's fairly easy to play, but it is fast. But you can do it with practice. :)