Asmodeus's Dragon Heist

I'm looking for advice on running Asmodeus as a warlock patron for one of my players.

While running a modified* version of chapter 1, one of my players touched a crystal orb and began hearing the voice of Asmodeus in her head. He offered her a pact in exchange for her service.

This worked out to my benefit, since that player had been thinking of taking a level in warlock for some time. She's interested in a personal relationship with her patron, if not necessarily a healthy one.

The issue is, I'm not sure what Asmodeus gains out of this, or how he would go about tempting a character that, while lacking confidence, is motivated more by helping others than any personal greed.

The Cassalanters are also about to give the players their own version of how Asmodeus tricked them and doomed their kids, so they can trick the players into helping them get the stone.

I can see Asmodeus manipulating both the Cassalanters and the character, and playing them against each other so they both come off losing something dear to them.

*Dragon Heist: Forgotten Tales on DM's Guild. It's a rewrite of some of the adventure that keeps things fresh for anyone who's played through WDH before.