Hi, as others have said, unfortunately there comes a time when the person with dementia needs somebody with them when going to the loo.
I have been at that stage with my husband for about a year now. His difficulty is mostly in remembering the order of things from pulling down pants, sitting down and actually doing 'the business'.
He is aware of the general process of cleaning up but loses track of what to do with the toilet tissue once used. If I wasn't on hand to talk him through the whole process it would end up anywhere.
There is a fine balance required to make sure enough support is given during the whole process without overriding the person's dignity or independence. I tend to let my husband do as much as he can, usually just standing by the door or just outside the room, pretending I am otherwise occupied.
One he has finished I pull off the sheets of loo paper for him so he can just concentrate on cleaning as much as he can, and I direct him to put the paper down the loo before I hand him the next bit. Eventually, if I think it is necessary (which isn't always) I step in at the end with 'you've done a good job, would you like me to check all's good?'
He hasn't refused my help yet but he doesn't come away thinking he has lost his ability to do the most part of the task.
His carers at the day centre have also been informed of his toileting needs should he ever need to answer the call of nature in their care.