This may be some form of hematoma formation as a purplish or violaceous discoloration suggests an underlying vascular cause.
Does your child have the habit of biting her lips?
Does she usually lick her lips?
Any previous trauma or injury to the area?
I suggest that you have this checked by your primary physician.This does not sound like an urgent case unless there are associated fever, rash, pain in swallowing and other symptoms.
I am constantly telling her to use her chapstick....she ALWAYS has dry lips....but this is like NOTHING I have ever seen before. I gave her benadryl before I put her to bed and she has an MD appt scheduled for 11am tomorrow, but it is kinda scary....and LOOKS horrible! No trama to the area. She has been without her 2 front teeth for almost 8 months and they are FINALLY growing back, but I asked if she had bumped her mouth or sucked on her lip...or sucked her lip into her water bottle when she drank and she said no. No fever....I checked again just now. She isnt complaining about any pain except to her bottom lip now (I think that is just dry & chapped because she has been trying to hide the upper lip). It is darker purple now and has spread to most of the outer part of her lip!