Future mother-in-law mad I didn't want her to help out after my miscarriage. Why's she upset?

I had a miscarriage a few months back and the only people I wanted around me were FH, my mom, sister and grandmom. I had a long, slow recovery process (my miscarriage was the result of having been hit by a car while crossing the street) and I felt ver fragile. FMIL kept haring me and FH, wanting to come to the hospital, wanting to come over and not giving me any breathing room. FH told her that I just really wanted my family there, esp my mom. FMIL shot back and said she was a mom and that was the same thing. No, it is not the same thing! My mom is my mom! She has been comforting me for years, knows me inside and out, knows what to say and not to say. It is not the same way with FMIL and I am very puzzled by her belief that she and my mom are equal and mean the same thing to me, when they do not. Why can't she get over it?