Lucia is Marjane's roommate at the boarding school in Vienna. Before meeting her, Marjane imagines that Lucia might look a little like Heidi.
When they finally meet, there's a huge language barrier between them. They try to find some common ground by sharing food with one another: Marjane shares some Iranian pistachios and Lucia shares… a Knorr soup. Um, thanks Lucia… for splurging at Wal-Mart… we guess. At least it's not Cup Noodles? And while Lucia isn't the roommate from hell, she still blowdries her hair at 6:30 every morning. We don't think Lucia means bad; it's just cultural differences and an inability to communicate on both their parts.
So the food thing might not have gone that well, but the girls do bond for real later on when all of Marjane's friends go away for Christmas. Lucia invites Marjane to her home, and her whole family is very warm and welcoming. They are some of the few people who don't treat Marjane like a terrorist: they're genuinely happy to meet someone from a different country.
It's kind of sad that Marjane gets expelled from the boarding house and has to leave in a hurry, because it means she never sees Lucia again. We guess good friends go as easily as they come into Marjane's life.