Ask her to rub potato juice and cucumber. It will definitely help. Also use Thrive co Sunscreen either she is at home or outside. Non greasy and contain SPF 50 which is good.

It will take some time for the tan to go away. She can go for de tanning treatments which will help a little. Ask her to use sunscreens on daily basis. She can try one from Thrive Co brand. It's non greasy and doesn't leaves any white patches, comes with SPF 50

You can use cucumber juice or potato juice .. it helps