Use 'Lithuanian' to recognize someone's national origin without implying citizenship. Though she lives in France, she is Lithuanian.
Pro Tip 2/3
Cultural Respect
Be respectful; 'Lithuanian' labels nationality and is part of personal heritage. The Lithuanian community celebrates their traditional holiday.
Pro Tip 3/3
Avoid Stereotypes
Don't assume personal traits based on someone being Lithuanian, it's a diverse culture. He is Lithuanian but doesn't like basketball, unlike many from his country.