I think different places have different policies. At least 24 hours since last vomit or diarrhea episode is a common one here, but diarrhea can easily lat 2 weeks in little ones with a stomach bug. You may want to check with the nursery what their policy is. The poop will be contagious for at least the next month so be vigilant about hand washing for a while, as they (and you) can get re-infected easily (strangely some stomach bugs are not like colds for example, you can actually catch the same one again, it takes weeks for immunity to build up). Also, see how LO is feeling. She may not be up for much activity for a while, and besides you may be sick by Tuesday as well. These things are damn contagious. Oh how I hate stomach bugs....