You're speaking to Dr. Michael Salkin. Welcome to JustAnswer. I'm currently typing up my reply.
Chrissy, while this necessarily must be conjecture without examining Poppy, I would be concerned about a cervical (neck) myelopathy (spinal cord disorder) such as degenerative disk disease (a "slipped disk") when both front and hind limbs are affected as you described in a middle aged cockapoo. Less commonly, encephalopathy (brain disorder) such as granulomatous meningoencephalopathy/GME or a steroid-responsive meningitis-arteritis will be responsible.
It would be prudent to have Poppy's vet take a look at Poppy at your earliest convenience. Keep her very quiet at this time - no jumping up or down or navigating steps - in order to avoid her hurting herself further. Please respond with further questions or concerns if you wish.
I understand. I can make one wrong move and my back can put me out of commission for a week! An intervertebral disk can prolapse or rupture in a split second. Please continue our conversation if you wish.