A little after she turned 2.5, my daughter started "to romanticize" all things related to her being a baby. I doubt your daughter remembers nursing. She may have recently seen someone nursing a baby; the idea of milk in boobies is odd and funny to her... or she probably is just more aware that you have different anatomy than daddy AND HER (remember, she looks down at herself and notices that she doesn't have them either)... Only mama has those fun squishy jiggly pillows... And hey, they're even better than her stuffed animals because as long as she's holding on to them, you can't go anywhere!!! You have to stay there with her! (Smart girl!)
When my daughter started this phase, I responded consistently (although not with anger), that "its not nice to mama to grab/touch her boobies", "its not nice to pull on mama's shirt (especially out in public)", "that's not nice behavior", etc, and you casually move out of her reach. She'll grow out of it.