Does she have a profile? Is she a member? If not, go to her profile and add her email address to the field for this. This will generate an invitation to join.
If she’s a member, or becomes one, you can add her email address to the profiles you want her to have access to. As said, you only need to do this on recent profiles as profiles for more distant ancestors are open.
There is a way to do this faster, if you are adding her to a bunch of profiles.
Hope that helps. Come back here to the forum if you have more questions.
(Edited for clarity)