I don't think Tempestus scions or sisters of battle can be considered "throw-away peons" by any means. and if she works in Mordia that is probably the most likely. Than again the Inquisiton does keep it's own battalions of Private and more 'run of the mill' stormtroopers for just this purpose. 

Also if I wanted to pilot something like a Sentinal. 

A- is that allowed?
B- can I modify my sential? Not crazy modifcations. But things like armour plating

My idea is either a Sential pilot, An enginseer or some form of other Ultra-light vehicle pilot employed by the guard. Like a Tauros or something. I was going to do the Valkyrie but Those aren't Cadian soldiers as much as Imperial Navy pilots. So ya.