Either my effort was really bad or her definition of commercial fiction and mine differ.
Or maybe your project just didn't appeal to her. Maybe she's already repping a similar project. Maybe she'd already rejected four similar-sounding projects just before yours. Maybe she has a particular aversion to the name "Andy" and that's the name of your MC (that's a joke, btw).
A rejection, whether fast or slow, doesn't mean that the work in question is necessarily bad or that the agent doesn't know what s/he is doing, and as long as it's not a fantasy query sent to an agent who only reps non-fiction it's nothing to do with genre, either. It's not personal. It just means that particular agent isn't interested in seeing more. That's all.
Another agent may feel differently. If the query and writing are great, chances are good that another agent will. I don't think there's a published author on this forum whose query for their published book(s) didn't get rejected by at least one agent; I know I've gotten a few form rejects from queries. Not every agent is going to be interested in every project.
Once you have 50 posts you can post your query in
Query Letter Hell (in
Share Your Work; the password is "vista" [without the quotation marks]) and we can help you with it, if you like. Meanwhile you might find it useful to start reading and critting other people's queries and pages; giving critique to others often teaches us a lot, at least in most writers' experience.