We have the same name :)
Just a few questions:
Does your grandmother have any underlying systemic disease like diabetes or hypertension?
Is she currently on any medications like corticosteroids?
Does she have any allergies ?
One differential for this is seborrheic dermatitis. This form of skin condition may be due to stress.It may also be due to temperature and weather changes.However, the definite cause of this condition is unknown.
What triggers your grandmother's rash?
Is she under a lot of stress lately?
Are there any changes at home or any discordance in her relationships?