Hello I am Dr. Joey. Thanks for trusting me to help you and your pet today. I am a licensed veterinarian with over 15 years of experience. I look forward to working with you.
This is, unfortunately, a common occurrence in cats as they age, particularly cats with longer hair. Sometimes it is a factor of arthritis and less flexibility to reach all areas of the body and then once matted they cannot care for that. Sometimes there can be an underlying medical problem that mades the hair greasier or abnormal and then more predisposed to matting.
I do have a few recommendations. First, if she has very large areas of matted fur, those will need to be clipped by your veterinarian or a groomer, if she is good at a groomer. If they are extensive and she does have moderate length hair, then a "clip down" or "lion cut" is probably going to look the best.
Second, if she has not been examined by her vet in the past few months and had screening senior wellness lab work (Complete blood count, chemistry profile with electrolytes, thyroid check and urine check), then this is a next step. This lets us know if there are any medical conditions we need to treat or help her with that may make her feel better and start being willing to groom again.
Third, for her coat directly recommend once the mats are gone to brush once daily or at least every other day. Small mats can be brushed out (your vet can show you the technique). And, you can start her on a fish oil supplement if her coat is not already greasy which may help reduce the level of shedding. However, not all fish oils are created equal and as a cat you will need to get something probably in liquid form that you mix with canned food or put over dry (here is a link for a good product: http://www.amazon.com/EFA-Z-Plus-Fatty-Acid-Supplement/dp/B001ENIJW8/ref=sr_1_1?ie=UTF8&qid=1442687130&sr=8-1&keywords=efa+pump).
If your vet finds arthritis then using a joint supplement such as Cosequin for cats (link: ww.amazon.com/Nutramax-Cosequin-Capsules-80-Count/dp/B000F4W02M/ref=sr_1_1?ie=UTF8&qid=1442687169&sr=8-1&keywords=cosequin+cat) works great; with Cosequin inside each capsule is well flavored powder you put over food once daily OR you can give as a capsule.
We have more we can do for arthritis, if needed.
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