In general, willing companions will not let you pose them. However, I have a special condition in place for Heather since she is your Ghoul. The "special condition" is handled when she first joins your team following the Elizabeth Dane quest. So if you are playing an old save game where heather was already on your team and then install the latest 1.41 patch... she may behave like every other willing companion. I tired to make my patches backwards compatible, but I think this is one of the bugs that got through.
In regards to fixing your current game, a quick fix is to enable posing for both willing and unwilling companions.