There is no conflict of interest and it’s very unprofessional in my mind. Should a hs teacher also refuse to write letters for all students applying to any college their child is also applying to? Should a sports coach refuse to coach any kids in the same age group as their own? Absolutely ridiculous.
The only valid reasons for not writing the letter are if the letter writer thinks they cannot write a good or informed letter or if the letter writer is given insufficient time and/or is genuinely overloaded with letter requests.
The prof is being petty and competitive: the daughter should be competing on her own merits, not on her dad attempting to hold OP back by not writing a letter. He is also a coward for calling the counselor instead of telling OP directly. Nevertheless, it is what it is and this person cannot be trusted to write a strong letter.
In academia, letters can make or break people’s entire careers, but this is not the case in undergrad admissions. OP will have many ways to shine.
I was in your position (sort of), if you substitute “conflict of interest” with “moved back to Russia and stopped checking his emails.” I eventually decided to have a research mentor write an EC letter, as he could speak to my mathematical abilities just as well.
If you have a figure like that in your life – someone from a summer camp, or a research project – then have them write a supplementary letter and use your physics professor’s as the academic one. Nothing will look fishy at all; from the prospective of admissions counselors you’re simply taking the opportunity to diversify your application.
Best of luck!
What everyone said. He obviously expected you to ask him, and he found a very gentle way to get the news to you that he did not want to do so. Do not push it. You have nothing to gain.