Yikes..... I didn't know what to say

I went to Legoland with my best friend  and his daughter....during lunch time she ask me if I could be her daddy's new girlfriend because her mommy treats him bad and doesn't like him 😒.... She's 7.  Although, I know how her mom treats him I never thought she had actually seen it! Her dad and I actually really love each other on that level but we've never let that be shown in front of his children.....what do I do?