My Ochem I lab instructor (not a TA---she has a Ph.d in Chemical engineering) agreed to write me a letter of rec. However, she recently moved out of state for a job (engineering related). I know most schools require that letters be written on official letterhead, but since she no longer works at the school, she doesn't have access to the letterhead. Would it be okay for her to use the letterhead of the company she now works for, or will this confuse adcoms? How important is it for the letter to be written on an official letterhead?