"If someone is having a special occasion at the airport Hilton then they can dress up.*
well yes obviously, they can. No one else will be though, and the question was "do I need to" not "am I allowed too"
OP mentioned it was a special occasion, she wanted to dress up and asked for suggestions, mentioned her dd was dressing up
Yes, dress for the occasion by all means. She also didn't want to dress up, or not dress up, the whole point was she had no idea what to go for because she was over thinking a non existent dress code
to then say the place she's going to doesn't need dressing up for is not kind
But it doesn't. She can go in a ball gown if she wants. To say the place she's wondering how dressy it is, "OP, there's people there in jeans and trainers, don't stress about dressing up on the venue's behalf" is not unkind at all. You are trying to project that people are explaining there's no "dressy expectation" at a particular venue, as telling her she can't dress up for her daughter's birthday. Again, wear a "ball gown" if you want, just don't wear one thinking that's what this venue requires.
Try this. I've never been to a Zizzi restaurant. It's my nan's birthday and she's booked us lunch. How dressy is it? I don't know what to wear. She's always quite dressed up and expect her to be on this occasion.
If I get a response, that I can wear what I like to Zizzi as most people will be wearing jeans, people are being "not kind" according to you.