The Veccavi Companion ride Hunters into battle with a suit of medium armor, with a shield for added defence and a sword paired with either a lance or spear, and if left unchecked can cause havoc among improperly prepared infantry and archers. They are fairly tough and skilled, being able to best Ravenstern Horsemen and Pendor Mtd. Men-at-Arms easily in an outright charge when using lances. However, the Pendor and Ravenstern cavalry troops and noble cavalry in general will often demolish these women after that first clash, either due to better armor, better weapons, better mounts or all three.
However, if one is lacking in proper cavalry, a solid firing line will prove more than enough of a deterrent as their mounts are only armoured enough to be hit-and-run units and a charge can often be outright stopped, with only the their better geared sword-sisters making it to you archer line. While Ravenstern Rangers work best in this thanks to the sheer range of their bows, any higher end/plentiful ranged troops will do. Tight formations of infantry can also stall them out completely, as such groupings can any cavalry attack, and end with them being quickly chopped to pieces; should they be dismounted you will also find they tend to falter rather quickly as well as the armor they wear doesn't hold up so well in an extended melee.
They may occasionally be found in prisoner stacks if Veccavian troops have been taking a beating in Pendor, and you may hire them yourself either through a mercenary company heartbeat quest or by hiring the Veccavian Renegades (requires negative relations with Veccavia). Also, if Boadice becomes a vassal, she will also have a number of these soldiers in her party.