You should really thank Nearly Legal ... and I suppose also Google for enabling me to find it in the first place.

You can still use 6A: doing so doesn't mean you have to comply with the additional requirements of a post October 2015 tenancy. It's pretty much a given that the council will go over it with a fine tooth comb on her behalf but as long as you can demonstrate that the tenancy started way before 2015 and you didn't take a deposit, there isn't really anything they use to block it, so it then just becomes a matter of time and patience.