I’m sorry your friend is dealing with this predator.
I don’t have much experience with Dantalion and Sallos, so please correct me if I’m wrong (that goes for anyone reading this), but I think Dantalion’s ability to change someone’s thoughts/mind can be helpful e.g. to have uncomfortable / unpleasant thoughts whenever they think about or obsess over the friend, and/or redirecting thoughts about the friend by giving them something else to think about and obsess over.
I’ve heard / read that Dantalion and Sallos like to be evoked together/ they supposedly get along well. Sallos is known for causing love, but the opposite is possible too - like weakening / removing love (to compare- and this has nothing to do with this, but Beelzebub can help with both causing and removing disease, but most people associate him with only the causing part, pestilence). You can also petition to spirits without having to do a full evocation.
A binding spell or freezing spell could also help, along with maybe some spellwork for protection.
@Mythopoeia has posted a few binding spells here:
Hope this helps