Hello. My name is Michael. I can help you with your question if you still need assistance.
In order to get into her gmail account, you will need her password. There is no other way to do it.
The only way you can obtain that is if she is deceased. Is that the case? If so, I can give you the appropriate information to request access. They certainly don't make it easy, but in some cases, it can be done. It really just depends on their current policy. Let me know and I can gather the information for you.
Google does allow you several options to handle the deceased user's account, including what you describe. Just be aware when starting this process that dealing with Google requires a great deal of patience. They are huge, and they don't take much of a personal interest in each "ticket" they are resolving. But this is something they take seriously and will act in what they determine to be the account holder's best interest. It just takes them a little time. Here is a link to the request page:
Pleas let me know if there is anything else I can do to help.