Follow this tutorial to learn how to transfer weights from posed armature to a mesh which requires the armature to be posed in such a way to make it look right.
This is useful mostly for game characters and when you need to retarget animations across similar armatures and need to maintain a rest pose like T-pose or A-pose.
In this video I show you how to setup the heeled shoe for a manuel bastioni lab character but it should work for similar cases. See the final result at 7:37
https://www.youtube.com/watch?v=49rajmR-Yhk&feature=youtu.be
You can also use this method if you are modelling clothes and shoes on a posed armature and need to be able to transfer the weights from the posed armature.