I'm small and just changed the skirt on them, but I'm no stranger to altering. It can be a bugger, but it's nice to have something custom fitted. That's awesome that you could do that for her. I'm sure she really loved those dresses!
The most fun sewing was for my DDs when they were little. I no longer sew now though. It's just too fiddly And too many steps now. I can pick up yarn and needles and go and I like that better.
ETA- I started sewing when I was 10 so I was we'll versed in it by HS.