I have a similar alter, although in my case she is about 9 years old, so it was a little easier for me to have compassion for her (I work with angry kids, so i thought of how I'd work with a client which helped me).
She was really frustrated because I never gave her the recognition she needed, never thanked her for helping me out. I think the first time we really connected was when I told someone out loud how I couldn't have survived without her to take over for me. I'm not comfortable being angry, and so when I repressed the feelings, I created her to hold onto those feelings. She 'knows' in her mind that she is not a likeable alter. That's not her job. Her job is to protect us from threats.
You may be able to help her out by thanking her for helping you. Even if it's not the best way, she does this in the best way she knows how. Next it might help her to reassure her that you guys are safe, that there are safe people out there.
Something that helped me from switching so often to her was that I could start to sense when she was becoming stronger and I would say out loud, write it down: I'm angry. Just by stating that it allowed me to realize that it was okay to be angry. If people are around and you're afraid to be angry, you can also just say it in your head.

Just some thoughts. i wish you luck with this, and hopefully you can connect with her and find some common ground. If she is agreeable, you could even make a compromise about when behaviour is okay, etc. It depends on the two of you, and what she will agree to. It has to be a bit of give and take on both sides.

xoxo
IJ