The understanding of the concept will come and will be all the easier for having been introduced to it at a young age.
Something that might help is to take a circle, measure the diameter with a string, and then have her wrap the string around the circumference of the circle and mark where the ends of the string are and count how many times she wraps the string around the circle.
It will give her a hands on explanation of what it is you’re saying.
I loved it when my kids got to the age where they could start to understand jokes like that. To me it indicated that they were growing up and actually thinking abstractly. A good sign.
We did some illustrations with a wheel drawing a line, but the whole ratio thing was still beyond her. She accepted what I was saying, but didn’t get the “why” of it.
Yes, kids starting to make and get jokes is a really fun time. She really likes puns on words that sound alike and often asks me for a joke based on words she thinks of that sound alike.