When do infants really get attached to their mothers?

My baby is 15w and doesn't care who holds her at all. I breastfeed her and am always with her even at night. I feel like I'm not doing something correctly because everyone keeps saying like "oh wow she is so good she doesn't care that she isn't held by you!" like she never cries or gets cranky when I don't hold her and she can fall asleep with anyone. I know they mean no harm by saying that but it makes me feel like I'm not doing something right 🙁 advice? Will she get more attached eventually?

Also I'm particularly concerned that it's because when she was first born I had a lot of complications and couldn't take care of her over very well (spinal fluid leak/ could barely sit up and some other problems like a catheter) and had the nurses take care of her in the hospital the few nights we were there.. I feel awful about it now since I can't imagine not being there for her. Could this be the problem??