Get a foldable step stool or ladder. It's usually two steps high and with a third hop she can be on the counter. I have two, mainly for me, but I leave them out for the critters. One jumps well, the other (Mr. Spunky) mainly hops and falls if he tries a major jump and always negotiates even a minor jump. Mr. SPunky uses the stools to look out the windows.

The steps are about $20 at a local store like Wal-Mart.