I get similar treatment sometimes and it makes it super hard if you’re not on your A game it just feels like a proper gut punch.
Try not to take it personally and be proactive about it.
The key thing I’d say is don’t lose your patience with it, as getting angry is just gonna make her not want to be around you.
Try spending more 1-1 time with her, take her out for adventures, go to the park even just for a few hours. Gives mum a bit of time off too so its a win win, (not sure what your routine is like) but on those days then see if you can do the whole bedtime routine solo after getting back from your adventure so bath and teeth followed by stories and bed try build that bond. find something you both enjoy doing together that’s a bit special.
I still get days where she’ll flat refuse me for mum, and long periods where it seems only mum will do.
but on the days where I spend more time with her she lets me in a bit more.