My wife was bitten by a tick and now has a large rash and joint pain? Is this Lyme disease?

Possibly. Go see your doctor. He/she can run tests to evaluate the possibility.
Possibly. I would recommend going to see a physician as soon as possible, the treatment for lyme disease is simple, but the effects of untreated lyme disease are severe and can cause chronic illness.
Perhaps. Lyme disease is due to infection from a specific type of tick. A rash can be the first sign of the disease. It has a characteristic appearance. She should be seen by her doctor as soon as possible.
Maybe. Lyme disease is transmitted by deer ticks and the bite is classically followed by a bullseye rash. However, not all who develop lyme get that type of rash. Ticks also commonly transmit other serious infections associated with joint pains, including babesiosis, bartonella, ehrlichiosis & rocky mountain spotted fever. Lyme tests can be inaccurate. Consult a doc who is knowledgeable in this arena.
Treat. Treat empirically with doxycycline. Earlier treatment gives better results.
It is possible. Depending where you live, and the prevalence of lyme disease in your area it is possible. She should see her doctor at once. If the tick was not attached for 48-72 hours, lyme disease is unlikely. The deer tick, which carries lyme disease, is very small-about the size of a pencil lead. The typical rash is red circles that look like a target.
Possibly. Not everyone who is bitten by a tick gets lyme disease. If rash or flu-like symptoms develop, it is important to see a doctor right away so that proper testing can be done. The treatment for lyme disease is a course of antibiotics. If left untreated, serious complications such as arthritis and neurologic issues can develop.
Lyme is possible. Lyme disease is a tick-born illness seen in many places throughout the country, and especially the northeast. The most common symptoms are the typical bullseye rash which is quite large, fevers, body aches, stiff neck, and especially pain in the joints. Anyone living in a lyme endemic area with the typical rash (erythema migrans) or other symptoms should see their doctor as soon as possible.
Tick borne disease. Rmsf, stari, ehrichiosis, anaplasmosis, tularemia and lyme disease along with other conditions can be transmitted by ticks. The type of eruption may assist in diagnosis, but testing is available and generally most practitioners will err on the side of safety and treat empirically while awaiting test results or clinical response. Let a doctor who has seen this before examine him. Hope he's better.