Why is my 7-year-old dog not eating, losing weight, and drinking lots?

She is getting to be consider a senior pet. Due to that they can develop diabetes or kidney disease or cancer or some other metabolic disease causing the weight loss. A vet is the best option to run blood work to check for these disease as some are more manageable than others. If she goes untreated, you may notice the weight loss continue and even vomiting or diarrhea ensue due to advanced disease. On average it is more economic to treat and manage a disease when they are healthy, so the sooner the better you can find a way to take Roxy in the better. Different clinics might accept different forms of payment, so it may be worth checking around