It is not unvegan to support a woman's right to choose.
If you believe that your compassion for other people should extend to other animals then you might be able to forgive the action of a woman who finds the prospect of her pregnancy unbearable. Not least because you don't despise your own human fallability either. If you have replaced your compassion for human beings with your compassion for other life-forms then this woman is a killer first and foremost and the suffering which may have brought her into her situation, or may arise from it, will appear negligible or non-existent. The second position, as an expression of psychosis, should never be confused with the reality of veganism in my opinion.
Truly, the meaning of non-violence is simple. It's applying principles to the messy complexity of reality which is the challenge...a challenge that being 'anti-abortion' singularly fails to rise to...I'm anti- cold Monday mornings - so what? Any fundamentalism is attractively straightforward because it shuns reality and that's why it cannot be taken seriously.
I'd merely suggest a 'deep reverence for life' should also enable a flawed human being to kill part of herself in order to survive mentally of physically in a deeply flawed world. I wish many opponents of abortion would focus their considerable angst on mitigating the conditions which lead to unwanted pregnancies rather than betraying their infantile morality by victimising one of the victims (the mother). When we have re-created the garden of Eden maybe we can sit down and agree that abortion is plain wrong.