My guess is: much the same how teenagers lose control of their bodies during growth spurts in their teenage years, having regressed to a young body - and so suddenly at that - it's gonna take her a while to get accustomed to her new body. We don't really pay attention much to it because the changes are daily but imagine having the mouth of a 6 year old again, you probably would not be used to the dimensions of your mouth/tongue, muscles and movement, etc either.