My 19 yr Old Sister Wants to be Maid of Honor

Hey ladies. So I have a little sister that is 34 and a little sister that is 19. My 34 yr old sister will not be anywhere near my wedding. In a previous forum I posted, I stated why. Some of you may have read it and a lot of you agreed and understood my reasons. However, my 19 year sister and I have no issues, we are very close. We recently lost our Dad this past August and we have been one another's strength. I have appointed my two BFF's to be Matron of Honor and maid of Honor. I did this because I know that along with those titles comes responsibility that I know my little sister has no time for. She works 2 jobs while going to school full time. She has been dealing with a lot of things since we lost our Dad and hardly has time for herself. I get on to her all of the time about taking a day off, but she won't. She has yet to take a moment to get fitted for her BM dress. So I know she does not have time to help me deal with a lot of wedding things. I do let her know details about the wedding, I send her photos, I ask her thoughts, I invite her shopping with me, but she either has no time or responds a day later because she is so busy. She has been super sensitive since our dad passed so I do my best to have compassion when it comes to certain things. She texted me the other day and said she feels left out from plans and wants to be MOH. I let her know that I send her all of the details before I send them to anyone else and that I would never leave her out. Ladies, am I wrong for not having her as MOH? Should I give her that title, but delegate the responsibilities to someone else?