dd has a huge mouth ulcer ...

[Roskva]

... just inside her bottom lip. I've put bonjela on it, but she licks it off. I've also noticed that she seems to chew on it with her front teeth: I don't know if this is what caused it in the first place, or if she does this because it's irritating her. Anyway, it doesn't seem to be healing. Any suggestions on what I can do, or should I just leave it to heal in its own time?

Any time I've used Bonjella on my own mouth ulcers they hurt like hell! I use Adcortyl in Orabase which you can buy over the counter. I find it very good. It does, however, have some steroid in it. It might be useful to talk to your Practice Nurse or the pharmacist at the chemist.