Hi @Frenchy163 and Assalamu alaikum.
Your daughter is fortunate to have such a supportive mum and that will mean a lot to her. I think whatever you do will be appreciated, as it's clear how much you love her.
The two Eids are times of great celebrations, and people will develop their own traditions for those, just as for other faiths' celebrations.
There aren't many hard and fast rules about what to do. Whatever you and she would like to do, enjoy it! We usually include a walk, a visit to the mosque, lunch out, present-opening, visiting family, etc.
Diet-wise, halal meat is important, as is no alcohol - sometimes food can contain small amounts of animal products like gelatine or of alcohol, so it can be important to check labels! Generally speaking, if something's marked as suitable for vegetarians and doesn't contain alcohol, it's probably fine.
If your daughter's going to be fasting while with you, she might like some quick and easy food for iftar (breaking her fast) and for suhoor (the meal before fasting). You and she could try batch cooking something like aloo ki tikki (spicy potato cakes), they're a favourite here! Dates are also a good choice, with significance in Islam as well. Drinking plenty of water is important too, and a nice water bottle can double as a small gift if you're wanting to.
It would have meant the world to me if my mother had come to mosque with me for an event like Eid. That might be something your daughter might like too?
Do you have a mosque or Islamic centre near you? If so, you could ask if she'd like to go for Eid prayers. If you felt unsure about what to do/wear/etc, you could probably contact the mosque and ask for advice - for example, some places will have separate entrances for men and women while others won't. Generally speaking, dress code is pretty much whatever you want from jeans through to long dresses, just covering arms and legs, and a lot of people will bring a scarf or hat to cover their head in the prayer hall. One thing to bear in mind, though, is that people don't wear shoes in the main prayer halls - if you'd be uncomfortable in bare feet, remember socks or tights!
Eid Mubarak to you and your daughter when it comes! Have a great day!