It's because she's keeping him on till she sees what Eugene'll do.

She's treating Eugene shamefully." "Oh, stow all that! Eugene is not so remarkably strict, you know." And Lord Rickmansworth winked.
"Well, we'll leave that out," said Ayre smiling.

"Tell him it's treating _him_ shamefully." "That's more the ticket.

But what if she says 'No' ?" "If she says 'No' right out, I'm done," said Ayre.

"But will she ?" "The devil only knows!" said Lord Rickmansworth.
"Do you think you won't bungle it ?" "Do you take me for an ass?
I'll make him move, Ayre; he shall give her a chaste salute before the day's out.