English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.
Sign up to join this community
Ngram says you're both more or less right
While until recently to was certainly the more common option, recently for has gained in popularity. In the end you have to go with what people actually use.
Although, it seems to me the the sentence itself is not idiomatic, and a native speaker would be more likely to express this in a different way.
We would use for here, in Standard English.
It matches this definition of for:
preposition
3.
a. Used to indicate the recipient or beneficiary of an action:
prepared lunch for us
https://www.ahdictionary.com/word/search.html?q=For
More important, of course, is thinking about the wisdom of correcting a teacher.
