All her life. What she shouldn't decide is the life of another, especially another person's life who came about through her own intentional actions. If you jump off a building, you fall. On the way down, you don't get to change your mind after taking your own actions. The time to decide not to fall is before you jump by not jumping. Some women want their cake and to eat it too. If you want the sex but without the children, simple: just get your tubes tied or only date guys who have vasectomies.
Every day by closing her legs to every passing Tom, Dick, and Harry and not being a wanton trollop.
The woman has all the rights possible. She has the right to avoid pregnancy if she doesn't want kids, she has the right to get fixed so she won't get pregnant, or she has the right to let herself get knocked up and to love the child, she has the right to stay home and masturbate, but she doesn't have the right to murder others. But if abortion is the only choice, at least do it by, say, the 16th week or thereabouts.