You may want to have this checked out. She could have HSV I (typical cold sore virus), stomatitis, or hand/foot/mouth. I know this from first-hand experience because my kids all had stomatitis (like hand/foot/mouth but only was in the mouth and around) at one point. Maybe she's chewing her lip because it itches? Either way, I'd at least call the doctor. This is very uncomfortable for children and can be treated. With the canker sores, do you happen to notice her not eating very well? I assume not since you didn't mention it but if she's not, there's something called "magic mouthwash" prescribed by doctors. It numbs the mouth if it's painful and is especially helpful to get children eating again if they're not due to pain. Yes, it's a topical anesthetic so it needs to be used sparingly and with very young children, instead of them gargling and spitting, you need to "spot treat" the affected areas. I hope I'm not reaching with this, I just know what I've been through and it sounds similar. ...hope I've helped.