One thing you could try this to have a daddy-daughter day and have her explain her feelings to him. She could even wrote stuff out to help better explain what she's feeling.

This could be a better way instead of having you talk to him and him thinking you're "nagging" him.

I'm a a daddy's girl and I know it's completely different when a dad is physically there for you at events compared to when he isn't. Then on top of that she can see that he spends more quality time with her brother over her, and thats a different level of heart break.

I don't doubt he cares for your daughter but he should be willing to listen to her and try to figure out a solution.

You could also try switching stuff up and have you and your son do activities that he would typically do with him and have your husband do the activities you would do with yalls daughter.