Unless your mother was a significant person in church history, this would probably not be the place for a personal history. I would recommend the Family History Library. You can upload a digital copy to the FamilySearch website and ask the library if they'd like a physical copy for their archives. You can always send an email to acquisitions and ask though. I do know they take personal journals.
I am one of those responsible for acquiring histories for Church History. We do take histories if they are written about Latter-day Saints. We prefer digital if they were created digitally. We love to acquire original letters and journals of members. We have a large collection of journals.
Kourtney's answer is spot on.
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