Should I accept Maid of Honour role?

[tiredviolet]

Help me!!!
I've been asked to be MOH for my sister in law in November and don't know if I should accept the role? I was so so so surprised to be asked because we don't have a close relationship (I don't even have her number) we don't see each other or talk regularly. The rest of the family are also surprised! My DH is best man for his brother and we have a 3 year old and 7month old (by Nov.) so childcare will be tricky on the day if we both have roles to do.
AIBU to decline the role as in not sure she has close friends or sisters to ask?

The MOH and other bridesmaids would usually be expected to be with the bride while she gets ready on the day though wouldn't they? So it could be the difference between getting breakfast and dressed etc with your children vs being in a room with the bride for hours while you all get your hair done, keep her company and help get her into her dress (and if it's one with lace at the back, that can take ages)