I'm sorry that your question wasn't answered in a timely manner. There are multiple body systems affected and so it will be difficult for an online vet to clarify which - or all - are most important. For example...
Scratching legs/paw...atopy (allergies to environmental allergens) or food intolerance should be considered
Problems getting up, sitting and walking...general weakness, profound anemia, advanced osteoarthritis should be considered
Watering eye...perhaps from seasonal allergy but there are too many ocular disorders that cause epiphora (watering eye) to list in this venue
Shaking (a pain response, usually), trouble walking/losing balance...general weakness, profound anemia, myelopathy (spinal cord disorder), encephalopathy (brain disorder) are rule-outs
Standing and trying to poop - both constipation and diarrhea can cause those symptoms
Loss of appetite - can be caused by too many disorders to list in this venue
I understand your financial constraints. Please see what you can do to have Missy attended to by her vet. She'll need a thorough physical exam including diagnostics in the form of blood and urine tests +/- imaging in the form of X-rays or ultrasound. Please respond with further questions or concerns if you wish.