I think you can help her the most by leaving the door open to forgiveness. I had the experience of learning that I had more than likely gotten infected by someone who knew. While there is no way of knowing for certain, since this virus can be dormant, I didn't have any antibodies when I was tested and was only with that partner.
We also had much more of a connection than just physical, and the whole experience of him not disclosing and never owning his actions to me, was the deepest betrayal. After the reality of the virus sets in, I think most people understand it is not so bad and not really worth it or the point to hold someone in contempt for getting it. Now that I have it, I sort of see it as the "cost of doing business". That may be a crude way of putting it, but it rang true to me.
Forgive yourself. It is challenging, but you do deserve your own forgiveness and understanding. Living in regret and self loathing is just a complete waste of energy and life.
If you haven't already, I think the best thing you can do to make things right, is apologize to her. Give her the chance to forgive you or not forgive you. That will be difficult, I'm sure, but she is just as vulnerable, if not more vulnerable than you are. If money has been something you have discussed than maybe, but I know in my experience, a conversation and if my partner had owned the lack of disclosure, my emotional pain would have been a lot less.
This is just my take, in any case, forgive yourself.