[G]

I'm sure you already know, but here is how it's done. Spoiler, I guess, "just in case"

SPOILER: show

Ashley

• Prerequisite: She must survive the events of ME1.
• After the early events of the game, Ashley will spend time in the Huerta Memorial Hospital. Visit her between missions, choosing Paragon responses (Upper!) to show her interest.
• Old romances from ME1 can be rekindled, or new Male Shepards can start fresh.
• During the early conversations before her injury, make sure to choose the Paragon options as well.
• Even when she’s unconscious in the Citadel, visit her and offer some kind words anyway. While there, you can purchase a special item, a Tennyson Collection, at the store terminal in the hospital lobby. You may have to wait until she’s awake to purchase and gift the special item.
• Visit her; during your first trip to the Citadel, after the mission on Palaven, and a third time before finishing the Tuchanka missions. Afterwards, she’ll be ready to rejoin you.
• After Tuchanka, and during the mission in the Citadel, you’ll want your trust high enough so Ashley will side with you during the ending confrontation.
• If you were in another relationship in ME2, you’ll need to apologize and confirm that you’re interested in Ashley.
• After she joins again, eventually she’ll offer to meet at the Presidium Commons. If she doesn’t push for a serious relationship, you can. With that, you’ll be well on your way to sealing the deal.