You need to clean your child. She doesn't get to say no to that.
What you're describing is a child with unbrushed hair, severe nappy rash and concerns about presumably unclean or too-small clothes. While active children can end a day with mud on their clothes and twigs in their hair, they shouldn't start a day like that. And while nappy rash can affect many children, it still needs to be addressed early and treated appropriately.
Go to the meeting, listen to their concerns and ask for advice/help. Then make and sustain improvements. Not doing this could lead to a social work referral.
Things you can start doing today:
Daily cleaning of your child. Bare minimum - top and tail daily with bath or shower (including hair wash) every second day; teeth brushing twice daily; hair brushed until all tangles gone morning and night and as-required in between; use baby wipes or a damp baby flannel to remove food and dirt as-required. Some people will do a bath or shower less frequently (eg twice a week), but at this point you need to get her clean and keep her clean as well as addressing a severe nappy rash, so you need to be really on top of this.
Clean and appropriate clothes every day - everything, including socks, vests, pants. It doesn't matter if they're from a designer shop or from the supermarket (actually, supermarket clothes can be really good for nursery as they often wash well and withstand active play), but they need to fit her, not have inappropriate things on them, and be clean. She also needs a spare set of everything in her bag for nursery so they can change her if needed.
Treat her nappy rash. Not doing so is neglect. If you aren't sure that the nursery's recommendation is the right cream, then go and see your GP and get one recommended or a treatment prescribed if needed. But you can't do nothing - it's uncomfortable and an infection risk. You also need to change nappies frequently and as soon as she's done a poo, and keep the area really clean.
If you're struggling to get on top of things, you need to make contact with your Health Visitor and ask for help. This is your child's health and wellbeing that people are worried about.