You have two options.
Presumably this is already a custom head you have added to heads.2da, so the logical approach is to load the head model into Max/GMax and adjust the vert positions in that area of the neck to move them back half 5-10mm, enough so they no longer clip through the collar.
The second option is to create a custom version of the armour model (since again I assume she has a custom row in appearance.2da) and adjust the position of the verts on the collar, pulling them out a bit.
Either would be a valid approach, but editing the head is the one I would suggest.