My roommate neglects his dog. Help me help her

I've read the separation anxiety guide, but it hasn't helped because the dog isn't bonded to me. So I can't do anything in the guide.

This dog is fully bonded to him. He's never home, feeds her human food, never trains her, and never takes her out for walks. I want to take over being her owner and actually start training her and walking with her and fixing her separation anxiety, but she won't bond with me.

She's fearfully reactive, and scatters at every little noise, every little sound. Every time my roommate comes home, she runs to him and he pets her for maybe 5min before ignoring her again.

How would I go about starting to bond with her? I'm home more than him, and I have more resources than him to train her.

Thanks in advance.