There is no doubt Heather does suffer from nerves/pressure/expectations. And as current US open junior champion/no1 seed and hometown favourite she had plenty of that this week. That's why I think Heather's transition into seniors will be steady but not dramatic to begin with.
At least finishing number 2 is still possible if she can win the Orange Bowl and defend her doubles points. It will take an unlikely set of results featuring Gavrilova and Njiric for Heather to lose her top 5 status (and better Junior Exempts than 6-10), though she has fallen below Babos to number 4.