"A Girl Like You." Erika and Annalise immediately form a close friendship upon realizing how similar their situations are from a certain point of view, and sing a very sweet duet together.
The novelization confirms what many fans already guessed: Erika gets out of debt because Annalise pays it off at the end, freeing her best friend from what would've been a lifetime of indentured servitude. And then, Madame Carp goes out of business because the castle quits buying from her — presumably because Annalise made it known to her mother how appallingly Erika was treated there. That's friendship.