I was going to say to try to have her go without a bedtime snack, but I see that she vomited before you started giving the bedtime snack, right?
Is the bedtime snack the exact same thing she eats for her meals during the day? If I was going to give a bedtime snack I would give her a small amount of exactly what she eats (and keeps down) during the day. If she continues to vomit I would give my vet a call for a check up.
These little ones can be so tricky with their tummies!
