Making a beeline for the ears

When Opium wants to play, she’ll often go for Nifty’s ears to bite her and/or pull her in a direction by the ear.
There are times that she hurts Nifty but Nifty never seems to put Opium back in her place.

Is there anything I can do to protect Nifty’s ears or to help Opium get over this habit ?

My guess is that Nifty will have enough at some point and put a stop to it. Adult dogs can be amazingly tolerant of pups but that tolerance generally decreases as the pup grows.

If she is doing damage, then you do need to discourage it although I'm not entirely sure how. Maybe try calling time on play every time she goes for an ear or something, so that she may learn that ears = stop having fun. Or not. Maybe...