I have a babylock regalia, which is basically the same thing as a handiquilter. I love it. I would definitely consider if you have a dealer nearby. even if not often used, I would still have it serviced once a year to keep it in good condition. and would take it in for a service check up after you buy it. not testing it out certainly makes it a risky purchase. I would consider the estimated yearly cost you are paying to rent and the potential cost of servicing the handiquilter now with possible parts and fixes depending on actual condition and the annual upkeep and maintenance. how many years do you have use the longarm to make up for the cost of it?
I considered the above things before I bought mine and determined that it would be a better deal to rent a long arm at my LQS. clearly I did not listen to that conclusion and bought one anyway! I decided the convenience of having it at home was worth the cost sacrifice.
maybe you can talk her down on the price because of the risk you are taking. if you can get it for 3000, then you have a 1200 dollar buffer to fix anything that may be a surprise.