I haven't read the other responses so I apologize if any of my advice will be repeats.
I'd say to apply good old plain Vaseline to the rash at diaper changes...then use powder liberally at every diaper change.
The Vaseline will prevent any further wetness from getting onto the rash itself, which is essentially why your daughter has a rash in the first place...from sitting in her wet diaper consistently. Using baby powder at diaper changes will prevent any new rashes from developing once this current one heals.
And continue the use of powder even after the rash has healed.
Powder does wonders at preventing diaper rash in the first place.
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