But that is completly in character for her.
She loved MC very much and she believed in him in that he was going to make all his business legitimate. When she understood that that was not going to happen, but quite the contrary, was going to be worse with all his business in Cuba and such, she decided to put an end to the relationship and having an abortion to another male son, which surely will be taken as another mafia member by the Corleone family.
She is not stupid, she is brave. And even then , it was not enough, since she had her daughter killed because of Michael at the end.
Unless...you have issues with abortions which is another conversation altogether.