Hi Pearl and welcome!
It sounds to me like yout MIL just doesn't get how strongly you feel about this. She certainly doesn't get the phobia. Many women just think us CF women are being silly. How could you not love a baby? In her mind, if she just exposes you to this child, you'll eventually change your mind.
I've had numerous proud parents/grandparents say something like, "Isn't he so cute? Doesn't he just make you want to have one?" to me, knowing full well I've NEVER wanted children and have been vocal about that opinion since I was a child myself. Like they seriously expect me to say, "Oh, yes! I thought I never wanted kids until I saw your little precious. Now I must have one!"
My feeling about kids is, I can take them or leave them. I have no desire to hold someone's baby. I certainly don't go out of my way to be around themm but I don't really dislike them either unless they're brats. I will not tolerate bratty kids. I don't mind being around well-mannered kids, but as soon as they get noisy and active, I'm outta there.
Perhaps you should tell your MIL about the phobia and anxiety. Tell her these photos she sends you literally make you have a panic attack. You said you got along well with her before. Surely she doesn't want to make you have a panic attack at work.
Take care,
Kim