Because a smattering of cells that might, or might not, eventually turn into a human being is oh so much more important than the actual human being within which those cells are found.
You act as if that was a random mass of cells. It wasn't. There is a well documented development profile for humans, from the fertilization and implantation of the embryo onward. Not a random "smattering" of cells, but an organized and growing human in whatever stage of development she killed it.
Well, she made sure they didn't grow to their full potential, and in that sense she may well have 'changed the world'.
She helped put it there (optional), and she killed it to cover for her own negligence. Way to go mom!
Maybe someone will do the same for the mass of cells that embryo found itself to have the misfortune to be formed in.
Or maybe someday she'll wish she had the company, love, and support of the one she so callously killed.