What I noticed in the Molland's scene is that from the way I remember it in P2, Anne has to walk because Elizabeth is once again being mean to her and excluding her, with Mrs. Clay apparently only being polite in offering to walk.

However, in the book it's obvious that both Anne and Mrs. Clay really *prefer* walking home to going in Lady Dalrymple's carriage, and oddly enough, Mrs. Clay seems to want to walk because it means being able to have Mr. Elliot's company.