You know how the conversation wheel is set up, yes? In that circular pattern? The upper rungs are paragon responses, the middle runs are neutral responses, and the bottom rungs are renegade responses. Answers on the left side of the wheel will get you more information, while answers of the right will attempt to end the conversation. If you wish to charm Ashley, you will have to pick the upper rung answers on the left side of the wheel. Ask her about everything in the Investigate section, and choose upper-rung answers for those too. It might take a while, but the relationship will develop. If you ever tell her she's out of line, the relationship will be terminated on the spot, since Shepard will say things to her that will make her revert back to a "professonal, not personal" stance on the relationship.