Arianni, if you'd believe it. That's right, Feynriel's mother.
There's actually some reasoning behind it, both in-game and meta.
In game, when I played my 'canon' Hawke, one of the things I rolled for him as a quirk/redeeming character trait was that he was not only devoid of elven prejudice, but elves were his 'thing.' He didn't care about Dalish customs or culture or history, per see, but he found them more attractive (and, possibly as a result, was willing to give them more consideration than others).
Arianni was a number of things he found worthy of interest- she was devoted to her family (her child), she was knowledgeable and respectful to others, and she was willing to take initiative to try and resolve her problems to the limits of her ability before asking for help. She basically hit it off with him just by being a decent mother, which he found respectable, and the fact that she was a single mother trying to take care of her child? Well, in my headcanon the fact that he knew/believed she would do anything he asked to save her child is the reason he would never ask anything of her. The fact that Feynriel looked up to Hawke was just icing on the non-existent wedding cake.
Which is where the meta- perspective comes in: I think a Bioware romance with a mature, single parent could be interesting in its own right. It brings up a number of themes and ideas that generally aren't touched on: it passes on young/first love for a partner who, for one reason or another, has either never had it or already seen it go by. It brings a partner's family, especially a child's concerns/perspectives, into play. It directly addresses the prospect of the protagonist entering into a family, rather than having babies ever after be somewhere off in the future.
Single mother, or single father- take your pick. I think it could be quite interesting.