K.C.
HFM is highly, highly contagious. I have heard many different things from different docs on when it is no longer contagious. Some say:
1. When the fever goes away
2. One week after the first sores appear
3. When all of the sores are completely dried up
4. When all signs/symptoms are completely gone
If you only just got a diagnosis, I would probably keep her out of school on Monday, even though she just started. The last thing you want is to be known as the mom who brought her daughter to school when she was contagious with HFM!
As for the little one, she's almost definitely going to get it, so I'd keep her away from kids now too. It can be contagious BEFORE any spots/symptoms/rash/fever appear.
They do not need to put things in their mouths to pass the disease along. Any contact - including playing with the same toys - can spread the disease.