With my DS he was posterior and engaged from 28wks onwards. I was induced at 41+3 and DS was born at 41+5, approx 41.5 hours after the gel was put in, and he only turned around with the help of the midwives the day before he was born as it was stopping me from becoming fully dilated.

Unfortunately his head got stuck against my pelvis and I was given a diagnosis of suspected CPD (Cephalo-Pelvic Disproportion) where the pelvis is too small for the baby to fit out of - in my case they thought that the lower part of my pelvis was smaller than the upper part.
I have since been told that there was a big chance that my DS had turned back around to posterior again which made him get stuck.

The placenta was also anterior.

With this pregnancy bub has been head down and posterior since 16wks, though not engaged yet, and the placenta is also anterior.

Having said all of that, anything is definately possible and your friends bub may still turn around. Like her I am also doing the Spinning Babies exercises as well, so FXed it will work for both of us

Sorry I couldn't be of more help.