Challenging problem with old boss

I’m having a lot of guilt and frustration around my old boss and an ongoing project we started together when we worked together. She is now at a different institution (no longer academic) and I also moved to a different institution and working on building my career. I had a different boss after her and continued the project with him. Now that we are working on getting the work published, I’m having problems navigating who will be senior author on the work. She no longer puts forward effort towards the work and the other more recent boss has been fully invested in helping. I want to make him senior author, but she is refusing to discuss changing authorship. I’m stuck on how to think about this because I think she is being unreasonable. I try to see things from her perspective with 3 kids and challenging new job. I just keep thinking she is being greedy in not giving up senior authorship for something she clearly is putting minimal effort into. Should I let her keep the senior position since she started me on the project, or should I push to have my newer boss be senior since he has done way more work towards the project than she ever did?