What theories might explain this person’s behaviour towards my baby?

FTM here with an almost 4 month old baby who I love very dearly, and obviously feel a great desire to protect. I am aware that, as a first time parent, i may be in over drive. But I am keen to understand what might explain a friend’s behaviour. The term “acquaintance” might be more accurate, but you get the picture.

Said friend is single, female, mid thirties, and keen for a partner and children.

I started to develop a few concerns when I became pregnant about the level of interest and investment in my unborn child - talking into my uterus, wanting to touch my stomach (asking me to unzip my trousers!) in the first trimester, when I was not even showing; talking about never leaving the country so they could be close to me and my child. Wanting regular updates about the progress of pregnancy, making offers to be my doula (she works in accounting and knows nothing about the practice), sending me pregnancy videos, advice, tips and baby milestones to watch out for. Jokes about breastfeeding my baby… there’s more examples I could give.

The baby arrives and cue the unbridled, inappropriate behaviour. Hogging my baby when offered a hold, being unable to break eye contact with them wherever they are in the room. Whispering things into their ear and making outlandish statements about how successful they’re going to be. The last straw was kissing them on their face, when they know full well the risks, and when they had been very unwell with a mystery virus.

Her behaviour reminds me of the moment a zombie “turns” in a film - the eyes glazing over and the rabid fixation and hunger for another human.

I have heard of MILs acting like this, but what kinds of theories could explain a vague friend acting this way? I am aware I could be in protection overdrive, but I am also keen to understand the science behind this as a way to put it to rest.