I had them, and my 1st brother, too ... so I always elevate(d) my kids' heads even while nursing, to drain the fluids down the throat and away from the ear canals ...
but on the back, even elevated, is physiologically most likely to get into their ears (I use(d) a sideways elevation: my arm).
I'd guess it's probably best to consciously choose to suffer through a re-training (you hold her while she bottle-feeds and goes to sleep, then put her down), knowing it will work after a while, and prevent the ear infections
I am against back-sleeping, but I am WAY on the fringe on that one (has to do with international concern that SIDS is related to anti-inflammatory chemicals in the matresses, and that mammals' organs naturally hang from the backbone instead of squishing the backbone, and fluids can drain out the nose) ... definitely I am only telling you "there is another thought to consider about backsleep," not "you should flip her over" ... that decision has claerly been put in the realm of life or death and obviously I am not an authority in your life ;)!