Why is Marilla having second thoughts about getting rid of Anne?

In Chapter Twelve, Anne has been at Green Gables for only three weeks, and though it has only been a short time, Marilla cannot imagine life without her.

“I will say it for the child,” said Marilla when Anne had gone to her gable, “she isn’t stingy. I’m glad, for of all faults I detest stinginess in a child. Dear me, it’s only three weeks since she came, and it seems as if she’d been here always. I can’t imagine the place without her. Now, don’t be looking I told-you-so, Matthew. That’s bad enough in a woman, but it isn’t to be endured in a man. I’m perfectly willing to own up that I’m glad I consented to keep the child and that I’m getting fond of her, but don’t you rub it in, Matthew Cuthbert.”