Help!

[CWOL]

Today I gave her a check for what I felt was the community portion of the last balance of a credit card we shared (but she is the account holder). I excluded what I felt was her expenses and paid only what was incurred for the family.
She started to question my calculations but I told her that's what I thought was fair and walked away. It did feel good to be assertive in these types of matters.
I have noticed throughout the weekend that she is very disrespectful of me. When I try to give guidance to S about sports, school, or other life lessons, she interrupts me and interjects her own opinions which are frequently factually incorrect. I have in the past told her to respect me and let me finish my thoughts. I believe she developed this pattern of disrespecting me as a defense mechanism since she is insecure about herself. How do I work around this while staying Detached? I don't want to get into a fight with her.