Hello, my name is***** and I have over 20 years of experience as a veterinarian.
I am sorry to hear that Ruby is limping, and I understand that you want her to be comfortable, especially because she is a service dog and your husband needs her help.
If she is eating and drinking normally and has no history of bleeding tendencies or a sensitive stomach you can give her buffered aspirin at home for a couple days.
In fact the only over the counter anti-inflammatory that can be used in dogs is buffered, enteric coated aspirin. Aspirin does cause stomach and intestinal irritation and ulceration as well as clotting problems so should not be given for more than 2 to 3 days consecutively and should always be given with a meal. If you choose to use it watch for lack of appetite, vomiting, blood in the stools or dark tarry stools and stop immediately if you see those. Do not use aspirin if your dog has liver or kidney disease or a history of a sensitive stomach or clotting problems.
The dose for aspirin is 5mg to 10mg per pound of body weight orally every 12-24 hours (about one 325mg aspirin for a 50 to 70 pound dog every 12-24 hours). Always give with a meal. Do not use for more than 2 or 3 days.
If you used the "mini" formulation of Ecotrin that contains 81mgs of aspirin per tablet, so four 81mg tablets equals 324mgs (roughly the same strength as one regular 325mg size). Your dose was appropriate for her size.
Long term for joint pain I recommend using a combination of a glucosamine/chondroitin product (examples are Dasuquin or Cosequin) and an omega 3 fatty acid (like 3V Caps or Derm Caps). I recommend an omega 3 fatty acid dose based upon the EPA portion (eicosapentanoic acid) of the supplement as if we do that the rest of the supplement will be properly balanced. Give her 20mg of EPA per pound of body weight per day. For example a 70 pound dog could take 1400mg of EPA per day. Omega 3's and glucosamine/chondroitins work synergistically and improve cartilage health and joint fluid quality and quantity as well as reducing inflammation. They can take several weeks to see full improvement but some dogs do very well with them alone. They are available over the counter.
Another option is a product called Duralactin. This is an anti-inflammatory product derived from milk proteins and it also has omega 3 fatty acids incorporated into it which can be very helpful. See this link for further information: http://www.duralactin.com/products_canine.htm
If that's not enough and her limp persists she should see her veterinarian for prescription drugs that are more potent. Veterinary drugs we can use include a nonsteroidal like Metacam, Deramaxx, Previcox or Rimadyl. If those aren't enough we can add another drug in the opiod family called Tramadol and/or another drug called Gabapentin. These drugs are much safer and more effective than aspirin. Aspirin used for any length of time will create gastrointestinal ulcers and clotting problems.
Best of luck with Ruby, please let me know if you have any further questions.