I've always wanted to know.

It has never been confirmed on panel. PAD is notorious for not playing well with others, so he never let her interact with Zeb Wells New Mutants title where Doug reappared. He also destroyed Rahne's character to the point that no one else wanted to write her before the universe was rebooted. Thankfully Guggs is writing her with dignity, but we have no indication if either Rahne or Doug will survive Secret War or if they will be together on the other side. PAD claimed to have plans to bring Rahne into his New X-factor book at some point, where she would meet Doug....but it was so poorly written and utterly directionless that Marvel flushed it.

If I had to take a guess, I would say that she does know, but after what happened to her son, she's just not ready to see him, or really anyone yet. Also, she probably feels it would be awkward, since he died saving her and she was going to marry Hrimhari and had a child by him. Of course Doug got frisky with a robot so......yeah, that would be awkward.