...it's not Sueish. A Sue is a character who warps the established rules and story of the universe the story is set in, not a character who has a certain amount of traits.

...but I don't really mind characters with angsty backgrounds - depending on how they're handled. I think some of the main problems come from when the angsty past is being used to say either 'no-one has ever suffered like she has! Because she is just that Speshul!', or 'look at how much horrible stuff she's been through! You should all love her and feel sorry for her!'. But I don't think that bad things in a character's past are automatically a sign of Sueishness.

If you're looking for some more detailed advice, you could try checking out limyaael's fantasy rants on Livejournal. She did a number of rants on angst (http://limyaael.livejournal.com/tag/rants+on+angst), including one on how to handle abused characters.

If one would expect him/her to not be the only one with that sort of background woe in this sort of setting, it's not Sueish.