It isn't as simple as a Queen or Lady telling the Knight what to do. If you read Small Favour, you find out that Fix isn't willfully going after Harry, he is even warning him as best he can, as he is under a geas and not allowed to directly tell him certain things.
They have manners of forcing Knights to do their bidding, against which there is no resisting, but mechanics-wise it isn't the same as a compel.
That is exactly what I meant. Also When Ebenezer tells Harry that Mab can force him to do evil, but can't force him to choose to do evil or something of the like.
Would that be something more like one of them using Summer/Winter magic to lay down a gobsmack of a Gaes using thaumaturgy, perhaps at evocation speed? Would it just be a social attack with so much tagged and invoked aspects it was irresistable? How would you lay that out. I love the idea of debt for power and it works great, even for Summer/Winter magic but if the Fae Ladies can already force the Knights to do what they want then it sort of drops some of the impact of debt. That said, being compelled in individual cases with no fate gain could be a bad enough consequence as it is.