She doesn't even need to think about it. The answer is yes, yes she does.

Not as a replacement for her daughter (there's no replacing a lost child) but because Astrid is delightful and she needs a home and Lynn is the obvious, obvious choice. Besides, Lynn has gotten all motherly and protective and it is now near impossible to undo that. It's just too late to turn back now.

They go shopping for clothes, Lynn converts her study into a room for Astrid (some of the bookshelves stay, but most of them are moved to the living room) and then life continues on. Cheerfully. Astrid comes with Lynn to school most days, and then they go read outside together. Lynn is noticeably more happy now than she was when Astrid first arrived in a basket. It bewilders a few of her students.