Is this a boundary or an ultimatum?

Last year my father had a stroke that he 100% attributes to my mom's treatment of him. Due to her mistreatment of me, as well, I blocked my mom last year for 3 months. I unblocked her after she agreed to go to therapy, with the understanding that if/when she stopped going, I would stopped engaging in a relationship with her. I made this known last year - that I would literally only have a relationship with her if I knew she was going to therapy.

Things went even better than expected, with both me and my sister noticing a considerable difference in our relationship with our mom. We were able to have regular conversations instead of being belittled or used as a therapist ourselves.

A month ago, however, it became clear something was off, and it turns out my mom has stopped seeing her therapist. "What's the point of going to therapy? All they do is 'yes' you to death."

Last night my sister called me hysterical crying after an argument with our mom. Tonight my mom inquired with me about my upcoming trip home for Christmas, and mentioned that I didn't seem my usual self. I mentioned that I was not comfortable flying home knowing she was no longer in therapy. I then reminded her that if she continued to go, I would have a relationship with her, but that if she refrained, I would not.

What followed was a long and hurtful tirade, which including her accusing me of giving her an ultimatum, and making it clear that she would not tolerate such treatment from her child.

Therein lies my question - did I lay a boundary, or did I give an ultimatum? And if I did give an ultimatum, is that bad? Last year was horrible for my family and the only reason any of us continue to talk to her is bc she started therapy. I find her stopping it a month before the holidays, likely knowing we wouldn't want to enforce the boundary if it meant jeopardizing Christmas, to be super manipulative as well. Thanks for any insight.