James follows!

She takes her good girl to the Room of Requirement (it seems ideal for secure conversations like this).

"What's going on?"

She explains in as much detail as she can. 

"So... a future time-traveler alternate universe version of our, uh, hypothetical daughter is here to fix the Dark Lord problem. And it sounds like you think she's kind of hot?"

"...Yeah." She pulls James in tighter, then rolls a bit so her girlfriend is on top of her - shielding her from the world. (Something she only does when feeling vulnerable, James has noticed.) The Room gave them a small, defensible space with low lights; perfect for Lily to hide her face in her girlfriend's shoulder. 

"And... It's... A lot. There's a lot I'm thinking about."

"Keeping that big brain busy, huh?" Forehead kiss.

Nod.

"...It's easier to think Ellie's kinda hot than to think about - that me having a kid. And like - why? In the middle of a war?"

"Do you want to try to answer that question or do you want to be distracted?"

...Hm, good question. 

"Distraction and then answer when I can think about it more cleanly?"

In that case, James can think of several ways girls can be distracting.

Very good girl. 

She's doing her best to be!

And her best is exceptional. 

Hopefully this helps Lily get to a point where she's able to put her thoughts in proper order.

She thinks it does...

James is here when she's ready to talk.

"...I've never thought of myself as - someone who'd have kids someday."

Hum.

"...I think I'd like to. Someday."

Blink blink.

"...You'd be a good parent." Unsaid: Lily absolutely wouldn't. 

"Hey, give my girlfriend some credit. She can do anything she decides she wants to."

Slight smile. "Maybe I could grow into it," she concedes. "But - still. 1980... That's really not far away. And the war was still on."

"You probably had a plan of some kind, if there is a prophecy and you found out about it."