If I had to guess, I'd guess that the Mothers don't have "vassals" as such.
The Knights *have*to* obey their Queen; and have a different, but also "subject/vassal" relationship to their Lady (according to Bob, back when he was explaining things to Harry in
Summer Knight).
I think the Knights owe...
something... to the Mothers. Damned if I can figure out exactly WHAT, though.
And as for giving a "gift"
*shivers* I'm pretty sure that can't be anything good. The Mothers seem to be anchor and bedrock; if they act, at all, it's because stuff has gotten seriously F'ed Up.
Also, I think the Mothers are older. They predate the Kringle Mantle, so they're probably not subject to those rules.
That said... You may be correct. Maybe she already DID give him something. The Blackstaff, for example, would be a pretty OhShit kind of "gift."