I agree with Brian . . . some pretty good advice. If you don't have the $$ . . . and she can't sell it at her price which seems way above what the value is . . . at some point, someone will sneak in and lowball her and it will be gone as she will tire of waiting. I think it's better to educate her on the true value and perhaps if you don't have the $$ right now, you could write up an agreement with her (to protect her and you) - make a deposit and pay her off over a few months.
I got in to a position of helping a widow out of a friend of mine a number of years ago - she had some nice military muskets but needed to dispose of them for money that she was lacking. I tried to get the most out of them that I could even though I wanted several but didn't have the $$ at the time myself. Another guy, who knew her husband, ended up convincing her that they weren't worth much and she ended up selling them to him at about 25 cents on the dollar. She needed the $$ and saw an opportunity to get some, even though I could have liquidated them in a couple of weeks at their true value and was working on several sales to some collectors I knew. I was ticked as she was really taken advantage of. Had I known what she was going to do, I could have given her the same amount of $$ the buyer paid her and then made installments over a couple of months until they were paid off.
Good luck . . . hopefully you csn work something out with the lady that is fair to both of you.
If a pair of '51 Navies were good enough for Billy Hickok, then a single Navy on my right hip is good enough for me . . . besides . . . I'm probably only half as good as he was anyways. Hiram's Rangers Badge #63