Thank you for your query.
What you are describing are not pimples
but seem to be prickly heat
. It is best to keep your daughter in a cool environment so that she does not sweat. By applying oils you may be blocking the sweat pores which may compound the problem.
Infected lesions may leave behind a hypopigmented area but they should become normal over a period of time. Hence my suggestion would be to keep the child clean and ensure that sweating is to the bare minimum.
I hope I have answered your query to your satisfaction.
Wishing your daughter an early recovery.