She certainly won't let you have the piano for less that half of what you paid for it so selling it makes perfect sense and if you sell it together you should be able to arrange to have a friend or relative buy it for penny's on dollar and then transfer it to you behind the scenes as a gift or for future consideration.

Pretty easy to be the best offer when you get to see all the prior offers. If the price goes too high, then just take your 1/2 and be done with it.

Don't try to be upfront about it either and figure you can just pay her a little bit more than the highest offer and she'll be OK with that. Rational doesn't work in these situations but if and when she ever comes to her senses and repents she'll be relieved you were able to "save" the piano from her foolishness.

The internet is 90% complaining and entitlement and I hate it because I deserve better!