No you don't have to prove it, she just must be aware that should she be asked by someone what happens if she's away she must have the answer ready of ''so and so can stand in for me''. You don't actually have to, just don't book work for those days, and don't say that to them!
I'm sure we didn't have an accountant the first few years either, it is advisable as you get larger as if an error is made, it could cost you more in penalties than an accountant would cost. Accountants take some responsibility on their own shoulders if they do the wrong thing so your partially covered, plus they probably wont do the wrong thing!
Have you got anyone else you could get advice from? i.e. the FSB or some other form of advisor?