Yes, if she has her own account, you can send her an invitation to link as "family and friends." I just did this with a friend because we want to share MM. Our trips only overlap by two days, so we don't have many shared plans, just a couple overlapping FPs. I could see all her plans, but I could not cancel/change them (and she could see but not change mine). It also allows us to view and download each other's MM photos. I was very nervous to even try linking because I didn't want either of us to accidentally mess up the other's plans! But there is no way that could happen.
In our case, however, we changed permissions to "my friend can view our shared activities," instead of "all activities" because it was confusing to see those extra ADRs and FPs that I knew were not mine.