When a cat starts eliminating inappropriately, it's either due to a medical reason like discomfort upon defecation, or the cause is behavioral.
First, it's wise to rule out any medical possibility, so it would be a good idea to bring your cat to the vet for evaluation, as soon as possible, and also bring a fresh fecal sample for analysis. This will provide more diagnostic tools for the vet.
If a cat experiences pain upon urination or defecation, she will come to associate the PLACE of eliminating--the litterbox itself--with that pain, and then choose to eliminate ANYWHERE else. Cats in this situation usually choose 'soft' materials to go on, thinking this will avoid the pain. Beds are usually favorite places.
In order to prevent your cat from returning to the places she's already soiled (if she smells it, she'll keep thinking they are appropriate toileting places), you can use an enzymatic cleaner to completely remove all traces of stain and odor. Nature's Miracle and Zero Odor are good products for this purpose, and can be found in most pet supply stores, and online. For more info and to view all related products (like laundry detergent), please see:
Cats can also sometimes start eliminating inappropriately if there has been any kind of change in their lives, schedules or environment, as this causes stress and anxiety. If the reason for eliminating outside the litterbox is NOT found to be medical, it would have to be treated as behavioral.
Cats are creatures of habit and do not take kindly to change. If you have had any new people added to your household, or if a 'usual' person has left, if you got new furniture, carpet, appliances, another animal, etc., or if your usual daily hours at home and/or away from home have changed or you've gone on vacation recently, any of these situations could cause your kitty stress.
Feliway/Comfort Zone for Cats, is a cat-appeasing pheromone which can help to calm stressed cats and curb urine marking and/or inappropriate elimination. It comes in both a spray and plug-in diffuser. The diffuser plugs into an electrical outlet like an air freshener, but has no scent to humans. For more information, please see:
Major pet supply stores carry Feliway, you can also order it online, and some vet offices carry it.
There's another product which I think may help you get your kitty back to using the litterbox--it's a clumping kitty litter called 'Cat Attract'--it contains herbal attractants which encourage use of the litterbox. It too, may be found in major pet supply stores.
You should have more than one litterbox, if you don't, already. Some cats prefer to urinate in one box and defecate in another. The rule of thumb is usually one box per cat, plus one. If you have a multi-story house, a box on each level is also appropriate and usually prevents accidents. Of course, keep all boxes immaculately clean at all times, as some cats are very fussy about this, too.
Your cat may be doing this as a 'marking' behavior, especially if she's felt threatened or stressed recently, by another pet or even a human in the household.
Keep in mind that first you should bring your cat to the vet to determine if the cause of eliminating outside the litterbox has a medical basis, and then the most appropriate treatment will be prescribed to help the problem, if needed.
I hope all goes well, and this problem is resolved
for you and your kitty, very soon!