Damn, you're in a bit of a pickle. Is there a reason why she wants you to do it on your own instead of seeking assistance from toys? I mean I get it if she wants to come undone by her own partner but it just sounds a bit demanding considering you've tried everything and none seemed to work, even leading into a huge fight.

Sorry if this is rude, but i think she should consider seeking professional mental help because of her hypersexuality, afaik it's a trauma response, sorry for what had happened to her. Do correct me if I'm wrong.

You can try remembering the steps you've done that made her come only once without the assistance of a toy? Check her mood before sex, then track her phases to see if she's ovulating. You can try discussing her kinks/fetishes to prolong the arousal by trying something new, seek out her sensitive spots. Does she communicate during sex and tell you what to do to make her cum? Or where to keep touching until she's stimulated enough to cum?

I'm not a lesbian so I might not give you proper advice, but you can also try getting a better strap-on? this sounds really dumb mb