Hi Marcia,
I think you and your daughter are going to have a wonderful time on your vacation together! I'm hoping that your trepidation is based solely on the idea of some odd thing happening to you that would require you to get medical attention. If this is the case, the first thing I recommend is making sure your daughter knows what a cast member name tag looks like. Should something happen to you, she should know to find any cast member and explain the situation. Likewise, if she gets lost, she should do the same. You can also purchase "temporary tattoos", like the ones found safetytat.com, for your child with emergency contact info, so a family member can be contacted in the event of an emergency.
If you are severely ill and feel as though you need a traveling partner.
Kids Nite Out, a childcare provider recommended by Walt Disney World, has caretakers who can travel in the parks with you. You must provide park tickets as well as paying an hourly rate for this service.
Hope this helps. Have a magical (worry-free) vacation!