Hi Mona,
Welcome to the Moms Panel! I think it's great that you're willing to take on "the World" even if your husband is unable to accompany you. I completely understand how hard it is to travel with children that have different abilities and desires.
Although I'm willing to bet most anyone would be willing to say "sure" I'll take her, I don't think this is something that I would advise. Not only does it put them in a potentially awkward position of accepting responsibility for your child, it could make your child uncomfortable especially if there is a long wait, or should the ride experience technical difficulties. In my personal experience I have had delays of an hour on an attraction before it was evacuated. I know if my six year old had been alone (or with a stranger), she would have been terrified during that wait.
I would consider looking into a service such as
www.kidsniteout.com which offers "parent helpers" that will accompany you into the park for this very reason. We used them on our last trip for in-room babysitting and had a fantastic experience.
If this isn't an option, thankfully there are a lot of things that you could all enjoy together. I know my kids were great about understanding that it simply wasn't safe or logistically possible for them to ride an "big" attraction that their younger sibling wasn't ready for.
Good luck with your trip!