I like your interpretation of Millicent here; she's compassionate, gentle, patient, and feminine despite how she might appear physically. The relationships she's formed with Vince and Greg -- the dynamics between all three of them -- are touching. There's a real sense of "times are hard, but as long as they stick together, everything will be okay" throughout the story. If anyone can survive unfortunate circumstances, it'll be the Slytherins.
This is also a nice exploration of the ways in which these characters were affected by many aspects of the war, from factors as broad as society's view of Slytherins in the aftermath all the way down to something as specific as the fire in the Room of Requirement. The Slytherin view of canon people and events is uncomfortable to read, but likely very accurate.
Really liked this bit: "Millie, I love it when you laugh. The way your face lights up. The way you don't do anything by halves. When you laugh, you whole body joins in. Your belly shakes and everything." He moved his hand to her stomach and pressed softly.
And also, love that Greg figured it out before they did. ;)