Hi Dear,
Welcome to HCM.
Understanding your concern.
As per your query white head blister on the corner of lower lip of your daughter is because of cold sores and viral infection(Herpes Or 
Influenza). It occurs because of lowered immunity of body. There can be other reasons also like previous viral infection which remain dormant and reactivate by certain triggering factor . Infection also spread from person already having viral infection.
I would suggest you to advice your daughter for shower in warm water , give warm compresses on nasal area.
- Increase liquid intake .
- Take over the counter anti congestion drugs .
- Take 
ibuprofen (if not allergic ) or 
acetaminophen for irritation ,pain and swelling.
- Do warm saline rinses several times a day .
- Apply ice pack on swollen lips and apply honey on it.
- Put tea bags on lips for some times and keep then moist with petroleum jelly.
If condition doesn't start getting better in a week (because symptoms will go away by their own in viral infection ) then 
consult Doctor for proper examination . Doctor may order 
blood test or swab test . He/she may prescribe 
antiviral drugs ( 
acyclovir) or antibiotics (if flu leads to bacterial infection).
Hope your concern has been resolved.
Best Wishes,
Dr. Harry Maheshwari