Ashley, who is only available to Male Shepards, is unique among the Mass Effect 3Romance options because she is one of only three who can both be Romanced for the first time in this game, or have a Romance from a previous game continued.

Can you romance Ashley in Mass Effect 3 if you didnt in 1?

Yes. You can abandon your previous relationship with Miranda to pursue Ashley in Mass Effect 3. As a rule of thumb, you can initiate a romance with characters returning from Mass Effect, who were romance options in that title, and new characters introduced in Mass Effect 3.