It sounds like your girl is suffering from over-grooming. Cats that over-groom often cause fur to fall out resulting in a bald patch. The skin is not inflamed and the area is not itchy. The most commonly involved areas are the flanks, inner thighs and the belly.
Overgrooming is usually caused by some type of stress in the cats’ life, such as a new kitten/puppy/baby, change of diet, underlying disease. It may be even caused by the neighbours new cat/dog!However, sometimes even though the behviour is started by stress it becomes habit and the cat continues to overgroom. If it hasn't already been done I recommend you have her checked out by your local Vet and have them run a full blood and urine panel in case the 'stressor' in her case is an underlying medical condition of some sort.
Even though this sounds like a behaviour problem by your description, without a full Veterinary skin work up (including impression smears, hair exam and culture etc) it is difficult to rule out some of the other causes of hair loss. Diagnosis of overgrooming is often one of exclusion.
Other causes of hairloss include:
- ringworm (actually a fungus), usually the bald area is ring or circle shape. Very contagious to other animals and humans who develop red circles on exposed skin
- flea allergy dermatitis (usually see small 'scabs' over the bald area)
- mites (demodex or scabies- can be seen under a microscope following a skin scraping)
- allergic causes
- even some types of skin cancer
I do recommend you take your kitty to the Vet for a skin exam to rule in or rule out these conditions. Behavioural overgrooming is treated by behaviour-modifying drugs such as Clomicalm, which can be obtained on prescription from your Vet.
An over-the -counter product you can try first is called Feliway. 'Feliway' is a synthetic feline pheromone, or 'feel-good' hormone, that comes in a spray bottle and a diffuser and would be the first choice for 'stress' treatment.
Hope this helps, let me know if you have any further questions.