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It is not very clear as to what your mother had.But there are only two possibilities .One that she had Herpes
labialis infection and other that she had a Boil near the lips.Both the conditions are painful and can cause fever
.I would go with HERPES INFECTION.
Herpes infection can lead to pigmented spots after healing and usually there are multiple such spots.
One needs a proper anti viral treatment here for 7 days,along with medicines for fever .As far as spots are concerned she should not worry too much ,as they might get resolved after few months.
And in case its a boil then she needs a course of anti biotic for 7 days.A macrolide
would be a good alternative.
Kindly avoid self medications and consult a dermatologist
for proper medications.