When someone consistently interrupts you

My mom is consistently interrupting me, especially when I am talking with my Dad. She will interrupt our conversation and start a conversation with him like he and I weren’t talking at all. When I tell her that Dad and I were having a conversation and she interrupted she ignored me and continued talking with him. Could a boundary apply here or does that not work? If so, could you help with an example?

I ran the model but I am having a hard time flipping this thought. It is pretty engrained. Could you help here?

C – Mom interrupted me when I was talking to Dad and began a new conversation with him even though I had just asked him a question.
T – She is always interrupting me and thinking what she has to say is more important.
F – I feel belittled and that she is being rude
A – I get upset with her
R – I avoid her