As long as she has an account and you added her official name to the reservations, absolutely. But only you will be able to cancel or change those reservations.
You're saying you booked FP's and ADR's for your sister in law. So I'm assuming she has her own MDE account and you either A) logged into her account and booked them, or B) you guys are linked in your friends and family settings in your separate MDE's and you made her stuff through your account by selecting her name (and anyone else) for FP's and dining.
Either one of those options, when she logs in to her MDE account she can see everything and can edit anything if she wants to
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