MIL seems to have found a new DIL. It's driving me crazy!?

To give a tad bit of background, I do not have a mother figure. I started dating my husband as a teenager so my MIL has been in my life for over 10 years now. I love her.

There is a coworker of hers who is attached herself. When my husband and I are in town to see the in-laws, she is always there for dinner. She stays in our bed. When my MIL drives down to see us, this coworker tags along uninvited. She was originally assigned to my MIL as a mentor program.

My issue is this--She is now decorating my MILs house with pictures of these mother-daughter outings. Any picture of my husband and me has been replaced with pictures of her at all the family outings.

It bothers me more and more. Originally it didn't get to me. I thought in a year or so, the girl would stop needing to be mentored. I thought the girl would be with her own family or date someone. My husband and I joked about her wanting to be the daughter-in-law and marrying my husband. But now that my husband and I have been married for 4 years, the fact that I'm not invited to ANY of these events bothers me. I understand if I can't go since we are a couple hours away, but to not even be invited and then have all the mother daughter pictures posted everywhere hurts.

What would you do? How would you discuss this? Am I just being insanely over-emotional or jealous? Or would this bother you? Or would it be natural to be invited to mother-daughter outings first, even if there is the possibility I couldn't go, with my own family before a stranger was invited? I won't talk to her about it if I'm just being jealous but replacing all my pictures and sleeping in my bed seems creepy to me. Off base?