Here's an alternative method if you find the ACW time consuming like I do .
1. In RB enter song chords ie your sister's song, using a skeleton style
2. Have your sister lay down a scratch vocal
3. Now start going through the PG content viz what you've laid down and away you go
4. when happy with song style and real tracks used, lay down the icing on the cake ie final vocals and any other tracks you want.

OM


my songs....mixed for good earbuds...(fyi..my vocs on all songs..)
https://soundcloud.com/alfsongs
(90 songs created useing bb/rb)
(lots of tips of mine in pg tips forum.)