That doesn't imply that Rosie bought the theatre at all - and her words aren't all that ambiguous.
She lives in Helen Hayes' house, that's what the first reference is to.
The theatre was sold - she was not the buyer. She, and other town people are obviously worried about what's to become of the theatre with the new buyers, and she doesn't want to see the theatre get run down, so she said she will buy it and make it work if that's what it will take to keep theatre in Nyack.
"If you are going to do something, do it well. And leave something witchy."
-Charlie Manson