Assuming she will transfer out of her stroller-as-wheelchair, and these items would be transported in/on the stroller -- then yes, they can stay at the boarding/unboarding location (wherever you are directed for that particular ride). The stroller will be pushed out of the way, usually visible to others though not necessarily supervised. Someone would have to have a lot of gall to take something from a special needs stroller loaded with medical equipment sitting in plain view of everyone else while you ride, but the possibility exists.
If the items can easily fit in a backpack or tote bag to keep with you, you may want to do so. It depends on your comfort level of leaving such items unattended and being without for a period of time.
As a note...some attractions themselves are longer than 10-15 minutes. You will want to research those (check the disABILITIES FAQ sticky) and decide how your family might manage those or if you'll need to skip them. Also if it's that important, have a plan in case of breakdown or delay on the ride -- considering all the ride cycles that occur every day, failure isn't common but it does happen on various rides and guests can be left sitting in the ride cars for a period of time.
Enjoy your vacation!