commiserations my friend it must seem like an impossible situation especially when you are running a full time business in your home.
I wouldn't know where to start . Just a couple of immediate thoughts though.
Is it worth trying two or even three litter trays at differant locations around the house. Each cat may adopt a differant tray which may help particularly if Willow is avoiding the tray because she can smell the other cats there.
Some cats are really fastideous ,she may be avoiding the tray because your are `skipping' rather than complete clear and sterilise every time. (note the horsey term there ladies !)
I don't know anything about animal behaviour other than what I watch on TV but it sounds like Willow has transferred to you and was never really weaned properly. This is exactly what happened to us with my ex partner's Dobie. It now follows her around all day and night and cannot be more than 2 foot away at all times. It is a real pain in the proverbial as she will try stand between you when you are talking or doing anything. Totally nuerotic.
![DOH! :doh:](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/doh.gif)
The princess also is over protective and barks all the time when anyone comes near .
Maybe therin lies part of the answer. Perhaps you need to be a little cruel to be kind as the saying goes and put her in her place .Make sure she realises that you are in charge not her and you don't need her to protect you. Looks easy on the tv but try telling your cat that is is no longer going to get `fed on demand' but at set times . I am having no sucess at this at all with Boo as I feed her all day long with prawns and ham
![DOH! :doh:](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/doh.gif)
Sounds like you need a short break from the situation anyway. Maybe a few days in a local cattery(thats the cat not you hee hee)
![Evil Laugh :evillaugh:](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/evillaugh.gif)
will allow you to sort things out at the house and prepare a strategy .Plus it will give an eeasier start to a new regime with Willow.
best of luck anyway