[Shane]

I agree that it's probably not about the dog, so I'll try to get a handle on the relationship side of things.

I guess my reaction would be based on how your ex normally handles things. Assuming that this isn't her first ultimatum, what historically has happened if you don't allow it to turn into a drama fest? Does she move onto another issues, dig her heels in and never forget, or what? If there's never been any way to reason with her about stuff in the past, there's no reason to think it's possible this time. If she's actually open to education and negotiation, that's another story.