How do you deal with a toxic roommate?

How do you deal with a roommate whose main goal seems to be finding ways to irritate you?

If she has a problem with one of my habits, I’m willing to understand and work on it. But with her, it feels like if something bothers her 10%, she makes sure I’m bothered 100%.

Sometimes she even ends up getting annoyed herself because she’s so focused on irritating me. She’ll deliberately do things she knows bother her, just because she thinks I’ll get irritated by it.

She even once admitted that she sits and thinks about how she can irritate us.

We were three roommates before, but one left, and she told me herself that dealing with this roommate was really difficult. She brings up our upbringing, families, and even our bfs/lovers during arguments just to hurt us.

She’s almost 10 years (30 f) older than me, and now that it’s just the two of us, I genuinely don’t know how to deal with her.

What actually works with people like this? Ignore them completely, set boundaries, or something else?