I am sorry to hear you are worried about Cleo. My name is Rebecca. I am a veterinarian and will do my best to help.
I would be surprised if weakness and trouble jumping was caused by her getting Greenies. I have not heard of that before, and it is not reported as a side effect in cats in the many years that cat Greenies have been on the market.
If she were mine, I would try to learn if she has a neurologic problem (weak in her legs because of a problem with her nerves or spinal cord) or an orthopedic (joints, bones, muscles) problem. Blood clots in her legs could also make her have trouble jumping.
I would start with a complete physical exam: look at her gums, listen to her heart, feel her pulses, test her reflexes, palpate her internal organs and lymph nodes, feel her joints and spine.
It is good she is eating and drinking. If her gums look pink, not pale, that is also a good sign. Can you take her temperature at home?
Does she go outside at all, and could have been injured without your knowing it?