Is the fighting a bad sign?

My wife and I have been trying to introduce our new kitten for months now with what feels like very little progress. We've let them sniff through the door, fed them together, given them treats, all of that. But they just cannot get along. If we have it so where they can both be in the same room, he immediately and continually just goes after her, and she hates it. But she typically refuses to stand her ground and assert herself, and instead chooses to run which causes him to chase her and escalate. I noticed she was standing her ground in her tree, so my thought was to let this happen so that she could establish herself as dominant, but I'm worried it's doing more harm than good. The main issue here is that our older cat has fiv. If she bites him hard, it could be really bad. So far she hasn't shown much intention to do that, but he really just keeps pushing.