Who is your character forced to interact with? If your character needs to go to work or school, then you have a whole host of potential characters. Even if you're sticking to your character's perspective very tightly, there are likely people that she sees every day who grow and change around her. If this smoking is the kind that takes place outside, then she likely sees the same people passing by regularly. If she doesn't have to go to work, where is her money coming from? If it's from somebody she knew who passed, memories may play an important role in her life. If she's on the dole (literally or figuratively), she has to interact with government workers or other patrons.
How does your character cope with not knowing people? If the character's really in pretty total isolation, she would likely find ways to add characters to her own life. I can't say whether they'd be two-dimensional or not, though. If your character has pets, maybe she's anthropomorphizing them. If your character watches a lot of TV, she may be developing relationships with regular protagonists, newscasters, and so on. She may have imaginary friends. She may have conversations with and imagine the lives of people she knows or used to know in her head.
Does having more well-rounded characters actually make sense? Finally, if none of those people really have an impact on your character in a way that works, maybe that's important. It's possible that your story needs to explore what happens when somebody is deprived of real human contact of any kind of depth or when they reduce those around them to caricatures.