I see nothing wrong with the minimal pre-flop raise in this situation. You got heads up with the chipleader with your aces which is wonderful, but what exactly were you thinking with the check in the dark? A loose player with a big stack is the absolute last person you want to give free cards to, especially before you see the flop. The great thing about being a player who always follows up a pre-flop raise with a continuation bet is that you can bet your big hands and get paid off. In this particular situation (depending on my image) I might put out a big pot size bet - just because it's the last thing you would expect someone with the nuts to do.

All things considered, it is unforunate that the player made a flush draw. A 1/2 pot-sized bet would almost certainly get called by a player in position with the draw. If you happened to be crazy enough to lead out with a huge bet with the nuts, the mistake would have been on her, not you.