Wasn't she found guilty in December of 2021 and sentenced in the summer of 2022? Who exactly would she have cut a deal with then?

If you have information that will let you cut a deal with prosecutors, you don't do it after you're convicted! Deal time is before the trial. You trade what you have (be it information or an agreement to testify or disgorgement of ill-gotten gains or whatever) before the conviction and sentence as a plea bargain.

And there's no way she can't make some damaging comments on the relationship between Trumpedo and his BFF, otherwise why did she end up in Club Fed?

To get her to come out and affirmatively state Trump was innocent. Trump was trying to squelch the Epstein files debate and was hoping that having Maxwell say that he didn't do anything would calm it down. He was being slammed by the innuendo that he was holding back the Epstein files because they had something incriminating in them. Maxwell saying Trump wasn't involved with anything helped him, irrespective of whether the innuendo was actually true. That deal gets cut whether Maxwell has any damaging information or not: getting her affirmative statement was the bargain.

If she had anything of substance that could really harm Trump, she would have cut a deal during the Biden Administration. She didn't, so she almost certainly doesn't.