oh, I feel for you!
As a mom and a preschool teacher, I have seen this numerous times. Starts off as a cold, then ear infection, they come back to school seeming to be better then a few days later relapse. Its the horrible germ cycle.
First, its probably being passed around from kid to kid at the daycare. Second make sure your daycare workers are keeping toys and play areas sanitized all day and at closing every night.
Its one of those things that goes with the territory of babies being in daycare. We tell all our parents to save there sick/vacation time at work for these long winter months. We send sick babies home all the time because they put EVERYTHING in there mouths, the germs just constantly are passed around.
Just stick it out. Make your baby as comfortable as possible and try letting her air out without a diaper for an hour or so a day. If she has an accident on the floor it can be cleaned up but it might help with her rash.
Some babies are just prone to sicknesses more then others.
Good luck and just remember it will pass.
Jenna