Wow, lots of questions!
Anne would have been escorted to the scaffold by the ladies who had waited on her while she was imprisoned, so Mrs Coffin, Lady Kingston, Mrs Orchard, her aunt Elizabeth Boleyn (nee Wood), Mrs Stonor and her other aunt Lady Shelton - see https://www.theanneboleynfiles.com/5260/cruelly-handled-anne-boleyn-in-the-tower/
After Anne's execution, the ladies undressed Anne and then gathered her head and body into a white sheet and placed it into an elm chest which had contained bow staves because a coffin had not been provided. We have to remember that Anne was executed as a traitor and therefore was not important so a coffin probably was not seen as important. I don't know where they disrobed Anne, it is not mentioned anywhere, but perhaps it was in the chapel. I also don't know how Anne would have gone about choosing her clothes.
Elizabeth was at her household in Hatfield with her nurse Lady Bryan, Kat Ashley did not become a member of her household until July 1536.