Brief Answer:
Observe for the general condition and also the lesion

Detailed Answer:
Hello

Thanks for asking on this platform

I have seen the image and to me it appears to be allergic rash.This allergy can be due to the contact dermatitis,any insect bite or allergy to other things like food item,pollen or medication.
Most of the time this kind of rash improves with use of anti allergic like diphenhydramine,fexofenadine or cetrizine.Application of mild steroid ointment also helps in early recovery.Please get these medication prescribed by a physician.
I would like to know if she has taken any sea food,any medicine or any history of known allergy.
In most of the cases the condition limits to skin itself and does not involve other system.
Still I would suggest you to observe her for any breathlessness,irritability, any change in voice,facial swelling or rapid progression of rashes.
If you notice any please consult emergency room immediately.

I hope this helps.
Please let me know if you have any more queries.
Regards

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