A possible romance option in Mass Effect 3 is Miranda, the (Ex-)Cerberus Agent. Halfway through the game she makes an appearance where you can select if you still have interest in her (provided you did in ME2) and later on she meets you in the presidential commons for this Scene.
When you meet Miranda in the apartment, she asks for your support. She is trying to find her sister and needs access to your resources.
Yeah, the scene is brief and not even sexy, but well … I was interested to see how those two would come along. Ashley, might be the prettier one, but Miranda is probably the woman that fits better to Shepard (in my opinion).
Added the first scene, where you meet her and tell her that you are still interested – save 0038