I have been testing her with Garrick. The timing is perfect, he goes stealth, she throws him to middle or back line still in stealth, then he hits someone for a a lot of damage. I don't know what it is, but Daphne has targeted Garrick first like 15 times in a row for me. I will keep testing, but it looks like you have to build a team completely around her.
I wonder if there is buff priority logic that favors Garrick over many others. Enrique also seems to target Garrick nearly every time for his haste buff if Garrick is still alive. Based on my limited experience, buff logic seems to have a solid order on which heroes get the buff. For instance, to get Enrique to consider buffing Octo at all (a really useful hero to hasten), I have to make sure that Garrick, Lingling, Tanya, Kong, Wraxius, and some others aren't on the team. Which means that practically it isn't worth arranging Enrique to buff Octo, which then means that Octo can't have synergy with Enrique almost ever, despite him being the one of the best choices for Enrique to apply his buff on.
Luckily with Daphne's ability, Garrick does seem to be a pretty good choice... although having used Garrick, that also feels like a death sentence for him too if the whole opposing party jumps on him after he murders someone. But I haven't seen it for myself.