Hi welcome to HCMForum. it appears to be tanning
. if it is fungal infection
there should be itching or spreadinp.
can be due to allergy
to metal used in the neck. or some thing else. like cream or deodarant. eosinofelia also some
times cause such changes. she may need to use skin lightening cream and sun screen lotion under the supervision
under the supervision of a physician. dont worry she will be all right.