Unless you don't have a proven pelvis, my hbmw doesn't do any internals.
I tend to think of an apprenticeship as happening under the direct supervision of the professional. I'd balk completely if my mw handed her apprentice the keys to my birth this late in my pregnancy. Then again, my mw's apprentice only started her apprenticeship weeks ago and has not been along for any of the ride until now.
I think the dynamics of the situation depend fully on how involved the apprentice has been from the beginning. If the apprentice is far along in her training, perhaps your mw has taken more of a back seat from the beginning, and thus, this has become the norm. If this hasn't been the case, I'd find my hbmw's absence in the very intimate last few weeks of pregnancy unsettling. It would completely unnerve me and I would definitely want to address it, directly, with her.
good luck to you!