I know this is typically a big no-no, but the problem is this one teacher in paticular. She’s the advisor of the club I founded (Astronomy Club. I want to major in one of the physical sciences) so she certainly knows my love of science very well. On top of that, she’s an alumni of my number one school (Cornell), which makes me think that her letter will hold more weight. I really want her to write my letter but I’m scared it will look bad that I’ve never had her in class.
Use it ONLY for a third, supplemental rec letter, if your target college allows one.
Colleges want teachers’ comments on how you did among others they have taught. Her being a Cornell alumna is irrelevant (you’d use her rec for non-Cornell colleges, too, right?)
If you sent this in as one of your required recs, I’d wonder – you couldn’t impress any of your other 20 teachers you’ve already had? What’s wrong with this kid?