you must not take my arm; you are a fellow. True, said I. I forgot; and you must not help me over puddless, as you did just now,
Referring to how she was going to go outside derssed as a man. It is not socially acceptable for a man to be arm in arm with another man. Mr. Fern was also not allowed to treat her like a lady. He should not help her over puddles and such. When they are on their walk. Fanny also realizes that suits are much nicer to wear than a dress or skirt in the rain.