Ex-girlfriend Wants The 2 Cats For Herself. How Can I Prevent Her From Taking Them?

My girlfriend and I just recently broke up. We have 2 cats we mutually agreed to get when we were still together. Fast forward until today and we're no longer together and she wants to take both of the cats herself and leave me with none. I love both of these cats with all my heart, and I will be heartbroken if she takes them. She previously had a cat she neglected and it died very young. I fear my sweet babies will have a similar fate.

I'm in Michigan. I paid for the most recent vet visit. I buy their food and litter. I'm the only one who feeds them, waters them, and changes their litter box. I have asked her to feed them once when I was late for work and she never did. I pay for their pet payment to live with us/me. Rent is paid by me. Vet records are mixed between her and I.

Does anyone have any advice on how I can keep these cats, and she can't take them away from me? I don't want them to have a similar fate as her last cat.