Even if it was forced labor, it doesn't necessarily mean that Kallen herself did not create the conditions for her to be selected as one. It should not be too hard, since she is a hot babe and an 11(even if only half) at the same time.

I really doubt a black knight member would simply be put to work after being outed, especially if she was still in possession of a knightmare key. Terrorists are extremely dangerous, especially in CG, and are treated with the utmost caution by the Britannians. I doubt they would put one in service of VIPs without even making sure she was unarmed (a km key is considered a weapon I think).