if you question friendship with someone, is it worth staying at all? help!!

So I've been friends with my very best friend for 12 years or so but she has changed a little bit. As it has always been, she doesn't accept anyone telling her she's wrong and so I'm not really allowed to say anything against what she says without getting angry looks or words. But lately she's been... I don't know how to explain it. Shes the same in some ways, but a different person in other concepts. I'm just tired of it but like I said before, I can't say anything. She won't listen to me. Even when I'm a trained veterinary assistant and try to tell her her cat is fat and unhealthy, lmao. She'll go ahead and tell me I'm wrong. Weve have had such great times and my favorite memories always include her as my partner in crime. But as the person she is today I have a hard time seeing any more times like those. They may be fun but not like before. Should I just tolerate this or should I turn a chapter? I just need advice because I don't have anyone else to talk to!