Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear about your girl's arthritis discomfort.
Ideally she would wait to see her veterinarian because the prescription medication your veterinarian has for pain will be much safer and work better than any over the counter medications that we take. In fact acetaminophen and ibuprofen aren't used in dogs because their effective doses are very close to a toxic dose in dogs.
The only over the counter nonsteroidal anti-inflammatory that can be used in dogs is buffered, enteric coated aspirin (like ascriptin). 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, OR if he has had any other steroids or nonsteroidal anti-inflammatory drugs within the last 5 days. Dogs that take a different nonsteroidal anti-inflammatory (like aspirin) too soon after taking another nonsteroidal (like carprofen, or metacam) or steroid anti-inflammatory have a much higher risk of organ damage or failure or gastrointestinal ulcers, which can perforate.
But if it has been at least 5-7 days since she took any medications, she is miserable and you want to try something the dose for aspirin is 5mg to 10mgs per pound of body weight orally every 12 hours (about one 325mg aspirin for a 35 to 70 pound dog every 12 hours or 2 to 3 of the 325mg aspirin every 12 hours for a 134 pound dog). Always give with a meal. Do not use for more than 2 or 3 days.
Be aware if you choose to use aspirin and it doesn't help your veterinarian will be limited on what they can give because there must be a 5 to 7 day washout period between different nonsteroidals or nonsteroidals and steroids.
You can try alternating warm and cold packs on her painful areas for 10 minutes at a time several times a day.
Make sure to rest her, no running , stairs or jumping.
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 that combination. 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 she is very painful she should see her veterinarian for prescription drugs that are more potent. Veterinary drugs we can add include a nonsteroidal like Metacam, Deramaxx, Previcox or carprofen. 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 your girl, please let me know if you have any further questions.