She was only a guest at Norland, and though Fanny is unlikely to throw them out, she can certainly make life very miserable for the family. "She was impatient to be gone, and indefatigable in her inquiries for a suitable dwelling in the neighbourhood of Norland; for to remove far from that beloved spot was impossible. But she could hear of no situation that at once answered her notions of comfort and ease, and suited the prudence of her eldest daughter..." It seems that there was nothing available nearby, and if they have to relocate, then living near kind and generous relations is better than living where they have no connections. I think it would have been imprudent to turn down Barton Cottage.