N.K.
If your kids get cold sores, that's a form of oral herpes and they will have it for life. Not the end of the world, but a nanny should know better. I would probably fire her for that. If you're not interested in firing her, then it seems like you will have to pick your battles carefully. Perhaps make a list of your dissatisfactions, then rank them from most important to least important. Then, address the first few. Once those are handled, then you can address a few more, etc..
As far as her doing too much housework, can you find her something else to work on? Our nanny does not wash our clothes, we're too picky. But, she does fold them and does a great job. She doesn't wash our dishes either, but she does unload the dishwasher. Occasionally we ask her to do other little projects during naps like organizing things or putting things in boxes to be taken to storage. Maybe your nanny could do some projects for you. That way you're channelling her energy. By the way, how does she have time to do all that stuff with 3 children to watch? That seems kind of surprising to me, especially if she's only part time. Oh, by the way, are your milk/meat dishes clearly labled? Do you think you could put the smaller toys away for safe keeping when she comes over? Good luck!