Kyle M has good advice. If she does sell by roadside, she should pick a fairly populated street but not one that has non-stop traffic. She could also try selling at your local farmer's market or flea market.
That's my primary business and I'm happy to help her. My number one tip is to grow a mix of three things when she first starts out. First, grow whatever is most likely to thrive with little care in her area. Second, grow something that no one else grows within a 15-minute radius. And third, grow something that's likely to bring in the most revenue per flower. Start growing those three types of flowers and she'll be off to a great start. She'll need to reassess every season because what's popular in the fall won't be what's popular in the spring.