YABU - your daughter wants you to be there to support her, why wouldn't you want to do that? It would be one thing if you had an important client meeting/project deadline, but from your OP you'd rather put work and saving your annual leave over supporting your daughter, how do you think that will make her feel?
I went to five open days when I was looking into Unis ten years ago, at least one of my parents came with me to them all, but both came to the first, just because I wanted and asked them to.
I didn't ask them because I was incapable of doing anything myself, or that I needed my hand holding for the entire time, or because I was incapable of catching a train and getting to the campus, but because I wanted them to be there and valued their opinion.
I went to the same private school for the entirety of my school education, my parents chose it when I was 3 years old and I loved being there and stayed right through to the sixth form. I had never had to make education decisions beyond what subjects to do for GCSE/A-level so going to Uni was a big deal, it was the first real decision I had to make about my own education and I could choose to go anywhere and study anything ... which for me was a bit overwhelming.
So when I went to my first Open Day, I asked my parents to come with me because I had no idea what to expect (I was the first person in my family to go to Uni and I'm the oldest child of the oldest children so I was the first one of my cousins to even leave school) and wanted some support.
They came along to the first one, and whilst they let me take the lead in the course specific talks, when we went on a general tour, my parents then asked the guide about practical questions I'd probably not thought of in the moment - average cost of living, public transport, practicalities of securing Halls, paperwork deadlines, 2nd/3rd year housing etc ... stuff I'd have probably never thought to ask, but were good questions to help with the selection process as a whole, and when I got home it was nice to be able to sit and discuss it with them and get their input.