Immersion and trust training for a lone female rat

[sorraia]

She is approximately two years old. I have tried having a separate cage for the other rats that I have introduced and have put it right next to her cage. I have also tried introducing her to other rats in my bedroom with the door closed while I sit on the floor and she does not like any other rats at all. I am rather nervous about the aspect of even introducing a neutered male to her. She pins other rats down and bites very hard, hard enough to leave open wounds. I am working on the immersion training with her now and she seems to be doing really well with it. She is a total sweetheart with me but no one else. When my boyfriend approaches her she just runs away and comes to me.

Considering she's around 2 years old, I'd probably just leave her alone. She's pretty set in her ways by now, and at that age it could be more stressful to introduce another rat than it would do any good.