New cat pooping on bed. HELP

Hope someone can help us.
We have 3 indoor cats and we just added a new cat to the mix. 2 days ago. The new cat is declawed and was rescued it was living outdoors for some unknown time. She sleeps in our bed all night but during the day she pees and poops in our bed. We are at a loss and dont know what do do with her. 2 of our cats hiss at her but dont fight with her. All I can figure is she is marking her territory. Please Help we have a baby also so wasing the bed and mattress every day is not a option. Thanks

I am sure lots of other people will have some advice, but the only time that this happened to us was when our kittens were stressed out and felt they couldn't get to the litter pan (we had just got them and we had some guests over - their litter pans were downstairs with us - we now have one upstairs and have not had this problem since). Maybe the other cats are intimidating her? Also, as a rescue, she has probably gone through a lot. I know a lot of people advocate trying to keep a new cat separate from the resident cats until they can really adjust.

I am sure others will chip in with more advice, but if you get to the root of why she is doing this, then maybe you can solve the problem!

First of all your cat is stressed. She should be confined to a small room until she is consistently using the litterbox since she is having this issue. If she doesn't like one kind of litter try another, start with unscented non clumpable, then move on to what you use for the other cats. If she isn't interested, try dirt from outside, then slowly more her on to cat litter.

The others gave good advice. I used Cat Attract litter and it has kept Cleo using his box.