I don't understand why no one (except the last poster) pointed out that the parts don't have to stay with the frame. Thus, you might spring for 105 right now, understanding that you may have to move the parts over later on.

OTOH you can get her Sora and tell her she needs to learn to do her own adjustments and maintenance. In my experience that's been the big difference between groupsets - not so much how well they shift (they will all shift well) but how much maladjustment they can tolerate before performance begins to diminish.