If she's a friend of your ex, it looks like she's waited a set duration before she asked you out, so odds are your ex won't complain about it.
However, hanging out with her will bring you into more and more contact with your ex. It's up to you and her how comfortable that will be.
Remember, friends before men. She will dump you if you try to come between her and your ex.
EDIT: used the wrong word there, had to fix it. "Proscribed" does not mean what I thought it did.
