I'll side with the OP Yip812, not that the opinions of the rest of us affect her life at all, nor that she asked for advice. As she noted, this was a "My free bike rides so well I put baskets on it and have a great commuter.", not a "How can I improve the performance of a department store bike."
For a 3 mile commute and leaving the bike outside, I'd say a free bike that fits is perfect, and it doesn't sound like a lot of time and money went in to brushing it with rustoleum. I really don't think she'd get better performance from a more expensive bike, and if it's a beater that's left outside I'm not sure she'd get longer life either.