"I do love the idea of going on a field trip. Especially one that could yield treasures like makeup and killer outfits. Is the storage area far from here? Is it a potentially perilous trip?"
Perhaps it was the idea of getting out and doing something with Sirius after being cooped up at home for so long that had her so giddy.
Had the comment come from anyone else, Lily might have just laughed it off. Having it come from Sirius was different, though. "I'm surprised, Sirius... I would think James and I having another child would be one of the last things you would encourage." While he might never have said anything about ho he felt towards James, Lily wasn't blind or stupid.
"I'll come to you when there's things I need to work through before bringing them to James, if you don't mind." She sometimes needed a sounding board. And both Remus and Sirius were akin to trusted advisors in her eyes.