I agree with the other posters in that unless she and your bro help you with finances it really is none of her *expletive* business. Maybe it was her way of saying she didn't want to go fabric shopping. If you felt the need to further explain you could tell her that you can't get fabric as inexpensively at home and wanted to take advantage of getting some deep discounts at the outlet if something struck your fancy. You could go on to tell her you are a grown up and perfectly capable of assessing your own budget.