Regressing

Sunshine had some litter box problems a few weeks back, but all was solved. Well, she is at it again. She used my sink as a litter box last night, and I have about had it now.
She is not ill, her litter box is in the same spot, she is not sharing it w/ another cat. She is behaving normal, eating the same food as always, and has been de-wormed even though she tested negative.
I am so frustrated. I can't keep her if this continues. I know a lot of you are going to think I am being cruel, but having my two year old daughter with her fingers in a pile of cat poop is not healthy, and I just can't deal with it.
Last time it happened I was told to confine her w/ her litter box until she started using it. I kept her confined for 3 days, then she seemed to be fine. She has been using the box since about 3 or 4 weeks now, and now she suddenly regresses!
Does anyone have any clue why she could be doing this?? I feel like she is being spiteful for some reason. I mean, she normally doesn't even go upstairs. I don't know what to do.
PS. Just as a note, I had a cat about 6 years ago that NEVER had an accident, and the kittens that I have always use their box. I feel like she is doing it on purpose!! I could accept it if all cats sometimes did this, but I've had several and never before have had a problem. Why is she doing this to me??????????

She isn't doing this to you because she wants to. Something is upsetting her and in order to stop this, you just need to figure out what. She may be very unhappy with the kittens and the stress is getting to her. In many cases, once a cat is spayed and she is no longer with kittens, they calm down.
How much interaction do the cat and your 2 year old have? Does she appear to be stressed around children?
Have you tried getting her a larger litter box?
Cats especially do not prefer using things with a flat hard surface. When they do this it is always for a reason. The hard part is finding out what it is. They cant talk to you and tell you, so you have to narrow things down one at a time.

Ok Sandie, here are the answers to the questions you asked:
She has a large litter box, it is plenty big for her. She has been using it for 3 months, and is plenty big. As far as being unhappy with the kittens goes, I don't think its that. She basically ignores them except once in a while ( like once a day ) she will let them lay with her. She is very calm and doesn't seem to be stressed by them.
As far as her interaction with kids. My kids dont' really bother her. My son totally ignores her unless she comes up to him to be petted. And my daughter will pet her, or try to play with her but she doesn't STRESS her in any way. Most of them time, Sunshine sits on my porch ( indoor porch ) on the window sill and the kids don't pay much attention to her.
On the other hand, she gets plenty of attention from my husband and me. We love on her when she wants it, she is fed well, kept indoors, her litter box is always clean, she isn't ill, she isn't "ignored" or neglected in any way.
I just can't even imagine what it could be to cause her to do this. I don't mean to sound cold in any way, believe me, but I am finding it very frustrating since there is no obvious reason for this. I don't know what to do next, any ideas???? Is confinement my only option, because I hate doing it, but its the only way to keep her from ruining my house!!!!!!! Help.

OH Sandie, I meant to say, there are only 2 kittens left. All the others have gone to their new homes in the last week. Do you think she is missing them or something???
They were 8 weeks and not nursing. And the vet ( a new one ) said they could go since they were healthy and litter trained.
Do you think there is a correlation between some of the kittens leaving and her accidents??

If you don't find any obvious aggrivations it could just be a case of constipation. She may have a slight problem with it. You can try giving her 2 moist meals a day, laxatone, or mix some of the hairball food with her normal food.