the narrative function she serves makes her difficult to ditch in favor of the much more interesting secondary character.

more to the point, without two characters at least, I do not know to get conflict and a plot.

Try a character profile. Pretend she is filling out one of those endless forms like at the doctor's office. Fill in all her answers for her. That's a good place to start with the basics. Flesh it out by thinking about her family (or family figures), friends and some experiences she has had that have been defining moments (think of it like one of those online memes: "describe your most embarrassing moment" etc.) Also be sure to think about her deeper beliefs, values, attitude towards issues in the world around her, etc. We all have those, and they are a big part of how define ourselves.

Next, think about her personality and the way she carries herself, and how that changes depending on who she's with. What's she like by herself, with her mom, at a job interview, running into her cheating ex boyfriend, talking to a small child, sitting next to a cute guy on an airplane, etc? How does she change when she's in her bedroom, at school, in church, at the grocery store, in a bar, etc?

Try to figure out what her wants/needs/motivations are. They don't have to be related to the plot. In fact, she will have more depth if there are parts of her that are unrelated to the plot itself. We all have things that we really want. I mean REALLY want. We'll do what we can to try to get them to happen. And we have things that we really DON'T want, and we'll do what we have to in order to prevent them. We usually have more than one, and sometimes they conflict. And usually life is complicated enough that there are obstacles.

If you have trouble with these things for a fictional character, try this exercise. Go through the above steps for a person you know. Or several people. Their 'characters' are already established, so you just have to practice identifying things about them and recognizing the relationships between those things.

That's a lot to chew on, but it's the fun part (also, it's easier than actually writing the novel!) Don't store it all in your head, write it down. Just like when we meet people in real life, we don't remember 100% of what we learn about them. In this case, you need to remember, so write it down.

I hope this helps. If you need brainstorming help or have questions as you develop your character, this is a great place to ask. Also, try the search function to see if your questions are already answered.

Good luck!

Edited to add: By the way, welcome to Hatrack!

Edited again for spelling.

I think I have the solution. scrap all my existing pre-conceptions about the character and start afresh.

the checklist approach doesn't work for me. it did as a teenanger, but not today. my approach back then would have come down to building up a person and writing about that person. my present-day method comes down more to finding an image, archetype and stereotype and filling in backstory as needed.

the building up approach reminds me of television series bibles, where you outline all the characters, the basics of their histories and their traits. not to knock that, in fact I can think of a project where that approach would work well.

I may try the exercise of "outlining" people I know, though, as it may kickstart some things.

Me? I ask questions. All day, every day. Why does that character do that? How would he react to this? What does that remind him of? Would she do this or that? Etc etc ad nauseum. I drive myself crazy with questions, but I don't ever stop asking them.

Also, people watching. I'm in grad school, and every day I eat my lunch in front of the main library, where a gazillion people pass through all day long. It's amazing what you can learn from personalities and how people interact just by watching their body language, even if you can't hear what they're saying. But conversation is very interesting to eavesdrop on as well.