As an older member she should know that need to proctet her account last hack attemp werent long time ago,makes no sense just after the account get sold the supost real owner come here asking for it back,as i said refund my bitcoins and i refund your account ,is the most fair thing i can do for you now.
Incorrect - you should have realised that the "staking" was only done very recently and her account was years old (it took me all of 1 minute to work that out).
You still proceeded with buying the account despite the fact that you should have known that it was very likely that it had been hacked (my guess is you thought that she had left and would not find that her account had been stolen).
You have no moral ground on which to walk upon as I have shown.
Just give up and give her back her account would be the right thing to do (for sure you can call out the asshole that sold you the account to make sure that they can't do that under the same name again).
You lost some BTC but the reason you lost it is because you didn't want to just create a new account and wait like everyone else (so you actually deserve to have lost some BTC for doing so).