No time like the present.
You can get a small fiberglass bow set for her or, if you're handy, you can make a bow out of small diameter PVC pipe. Figure out how long it needs to be to give her a draw weight she can handle, without dragging the ground when she shoots. Glue a wood plug in each end and insert a round head wood screw into each plug for nocks. (The kind of screws that have about a half inch of unthreaded shank under the cap.) If you want to get fancy, you can paint the pipe and wrap the grip area with tennis racket grip.
If you're even more handy, you can whittle a selfbow out of a board. For little tyke bows, you don't have to worry about following the grain perfectly and all that. Just keep whittling until it's a draw weight she can handle.
A few Easton Jazz arrows, or some fiberglass ones, and she's ready to go 3D'ing with you.
Keep it fun and safe.