Luna spent a lot of time by herself. Not for any particular reason, but she'd spent a good portion of her early years at Hogwarts by herself. As she slowly made more friends, though, she found herself wanting to spend time with them. And she genuinely enjoyed her time with Anakin.
If he'd asked, Luna would have agreed that R2 should probably stay home and have a day with BB-8 or something. Somehow technology didn't seem wise, and Luna left her phone at home too.
At the small smile, Luna returned the smile. "You're welcome." Once they stepped through the portal, she asked, where would you like to go?"