Why would his ex send me a friend request?

I’m due with our first baby any day now. Yesterday, my fiancé’s ex girlfriend sent me a Facebook friend request. I don’t know her, never met her, and she is not a part of or lives. However, she is still fb friends with my fiancé and his mother who are all posting about me and our unborn baby. She has even liked some of my pics that have been shared to their pages.

I don’t feel comfortable accepting the friend request, because I feel like she might be just being nosy since my page is on lockdown.

Why do you think she’s friending me??!