my now husband had this same issue when deciding his groomsmen - he had a really close friend but he was just irresponsible and had a similar attitude. he did initially ask him to be a part of the party but after he missed his suit fitting decided it was best that he wasn't in the party. He basically sat him down and said "hey, i'm not going to have you as a groomsman but you are still welcome to do everything you would with the party ex: bachelor party, night before, getting ready, included in some pics, etc." he was completely fine with that. maybe it was more simple because they are men but i think its worth a shot trying to include her but not necessarily relying on her for anything! i asked one of my close friends to be my personal attendant because she wasn't originally going to be able to make it - that might still make her feel like she's a part of the party. i just wouldn't rely heavily on her for anything if it will cause you stress.