Sorry it’s not a movie, but I’ve been racking my brain for years to find this and your site has always been so helpful. A show aired in the mid 2000s with a bookish red-head girl as the lead. I think she really liked plants or animals, something along those lines. She had a stepbrother who was supposed to be cooler and always cracked jokes (I swear he was on Degrassi, but not sure). The series may have been Canadian and had a quirky vibe. It was never really popular iirc and may have been on for like a season or 2. Not Life with Derek.
Help if you can!