I would not concern my child. I would feel as if I was laying a burden on the child.
Children want and need to know parents are capable of providing for their necessities and their needs.
I would tell her that medications are to help us feel well and to stay healthy. And aren't we so lucky to have medications to keep us healthy!

That's really all a child needs for reassurance. A brief statement that says "Everything is okay and I am fine."