Configuring preferences and options in Outlook.com
Hi, I'm Diane and I'm happy to help you today.
You can't do anything from your side.
Does she have the other premium options? does she has an address with the custom domain added to her Microsoft account already? Check at account.microsoft.com.
You can try removing her from the share and resharing with her.
If you have any questions, please don't hesitate to ask.
-- Diane
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