OTA vs. booking direct doesn’t have anything to do with accruing miles. Your operating carrier (you haven’t mentioned your flight #) and your fare class (E, L , S, M, Y etc.) determines that.

In your case what I think is that while you booked economy saver at the same price they were tickets in different fare classes. For instance your ticket might have been in L fare class which is not eligible for miles in KF whereas your sister’s economy saver could have been in S fare class which is eligible for accrual in KF. Hence KF is refusing to credit your miles. Do check your flight # and fare class and share that. Those are the only two things that determine whether or not you’ll earn miles.

Also asking for the BP is standard silly response (completely outdated and impractical in today’s eBP era). Sharing your ticket copy will help you get your miles credited (as long as you’re eligible)!