Toph may have had to work hard to be both a mother and a father to her child (Lin's dad's never been mentioned, so maybe Toph was a single mom) but all those who think she wouldn't be a good enough parent are DEAD WRONG! she knew when to be tough, and when to be a nurturer
I honestely think Lin's dad's one of the officers that worked with Toph. I mean, I'm sure she worked a lot and spent the whole day with some powerfull benders, most of them man, teaching them to metalbending... She was beautiful and strong, I bet many of them fell for her, maybe one she loved back...
there's never really any indication of who Lin's dad is. It's probably gonna be like the Ursa mystery of the original series... what I meant in my comment was that Toph probably had help from the Gaang to raise Lin
it is said that 'it takes a village to raise a child'
and I'm sure that 2 non-bending warriors (Sokka and Suki), the fire lord (and fire lady if Mai stuck around) a waterbending master, a contortionist (Ty Lee) and the Avatar can help a blind earth/metal-bender raise a child.
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW. this makes me feel like ten times more sad that she actually did lose her bending, as i said AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW