You tell her that it's none of her business and end the conversation.
You venting to her does NOTHING.
Even if this ends at some point, you will have to coparent together and trust me, peace is better than war in that scenario.
You don't have to like what she did. She doesn't have to like what you did. Right now the other partners activities are the not the concern of the other.
Take the high road. The other road is full of regrets.
Bill
"Don't tell me the sky is the limit when there are footprints on the moon."