Replacing a counselor's rec letter with an assistant principal?

I go to a big school and my counselor really doesn’t know me. However, one of the assistant principals knows me well since I work with her on school activities. Can I replace my counselor’s with the AP? I know at some schools the counselor sends in everything but my school is split so one person is in charge of each. The registrar sends in the transcript and the counselor sends in the rec letter and school info sheet. So, I don’t know how to have the counselor send in the stuff aside from the rec letter. How can I ask my counselor without offending her?

Or, would it be better to save my AP for an additional rec letter in case of deferral or wait-list? And just have my counselor send in the normal one?

No you cannot choose who writes your guidance counselor recommendation. I would not even ask. Many schools do accept one supplemental LOR which is typically non-academic in nature (ex. a coach, boss, etc.) so you might consider a letter from the AP in that role.

The difference is when a school routinely has a principal or AP write letters in place of a GC. But not knowing the GC well isn’t a good excuse. You could get to know the GC.

Another option is, IF you are close to the AP, to ask him or her if willing to give some input to the GC. At some high schools, it’s common for teachers to write notes for the GC that serve as input.