Wow for that price and the offered infrastructure it sounds like a great deal. Perhaps she has a list of barn rules and a contract you could check out before deciding. Can you get some references and just discreetly ask around to see if other professionals know her and her operation? What does she do with her horses--compete, breed, train? It sounds like a professional operation and shouldn't be that hard to check out with a little detective work. Good luck.
I have 2 round pens and a "batters box". They are the portable galvanized panels which I love. They are easy to transport and set-up and were relatively inexpensive. If I ever don't want them anymore they can be re-sold at a good price and require no maintenance whatsoever. They look the same today as when I got them 5 years ago.