I may be way off the mark and I'd be very interested to know what others have to say but is it possible that it's an anxiety driven behaviour? Perhaps there's so many possibilities that it's overwhelming and she's not sure what she could have and how to control for the things she potentially can't have, so she needs to try for everything?

If this were what's driving it, I'd then assess the anxiety (are there any other stressors there that are making her amxious and increasing her need for control? How does it manifest for her in terms of thoughts, feelings, bodily sensations... what helps, how does it change when you say yes versus when you say no....), raise her awareness of it and teach management strategies and then set very firm, predictable boundaries around what she can and can't have. This may be to the point that you have to write down rules about things she can and can't have when out and how 'excess' requesting will be managed. Unpredictability can be very stressful - but is just in the nature of normal life. Sometimes you can go to the Bunnings playground, sometimes you can't. She may need it to be more planned than this so there's not so much room for the 'maybes'.