I went to Clarion & live in Pgh so I'll stick my nebby nose in.
I think Theta at Pitt only closed a year or 2 ago. Some nationals have a rule as to how many years a chapter must be closed before they'll reopen, or that all the closed chapter's members must graduate before they reopen.
As far as switching nationals, BIG NO NO. All the NPC sororities have a mutual agreement to not "take" chapters from each other. The only way they could eventually switch is to go local, wait till all the girls affiliated with national #1 filter out, and then go Theta. And by then it wouldn't be any of the same people.
I know there are a lot of active alum chapters in Pittsburgh, so if your friend's group is having trouble, PLEASE urge her to get in touch with the local alum chapter. They can be a lot of help and the last thing anyone wants to see (especially around here) is another chapter closure.