Hi, Christi! Conducting business or attending a conference at the Happiest Place on Earth is unlike any other experience you've had, and bringing your daughter along makes it even better. Yet, for that length of time each day and for that young of a child, I would consider bringing a grandmother, aunt or sitter along for the trip as well. You can certainly check into hiring a sitter from Kid's Nite Out -- a local childcare service which can provide someone any time day or night. They can be contacted at 407-828-0920. However, it may be more enjoyable (and even more cost efficient) to have someone she knows with her to enjoy her time at WDW while you're at your seminar.
The Children's Activity Centers (located at select deluxe resorts throughout WDW) open at 4 p.m. at the earliest and stay open until around midnight. They are designed to provide grown ups with group childcare options for evenings out. There are a few
other activities that provide entertainment for children (without adults) during the day, but they usually only last a couple of hours.
Therefore, my recommendation is to bring another adult with whom your daughter will enjoy spending her days -- either at the parks, exploring the resort areas or relaxing by the pool. I think it would be worth it for your peace of mind as well! I hope this helps you plan. Have a wonderful day and a magical experience at WDW!