5 Year Old Started Peeing and Pooping Everywhere

I guess I would look at why your sister moved in with you. Was there a divorce or break-up with the five year olds father? There must have been a significant reason for the move. Look at the reason and you probably have the answer to "why". Children react to things they have no control over by taking charge of what they can control.. like where to relieve yourself. Have the little girl checked out by a pediatrition. He will probably recommend a good counselor who can give you behavior modification techniques to use.
In the mean time you might try giving her little things to make choices about. Tell her that big girls who use the potty get to choose what to have for lunch or which playground to go to or what stories to read. (just examples). Try not to give a huge reaction when she does pee or poop on the floor (easy to say, huh?). When you do it just feeds into her feeling of controling the situation. Clean it up and reinforce how you wish she had gone in the potty so she could have chosen "what book to read ",but maybe she will next time so she can choose what "snack to have" etc... giving her a little power in simple things and downplaying the negitive might help.

I know this sounds obnoxious, and I don't mean it to be, but have you tried punishing her?? Five years is old enough to understand consequences.

i would try takeing things she likes away she is old enought to understand why you are doing this and was ther a termatick even t in her life and if so i would try talking to a councler about this to see what they have to say. my oldest did some thing simmilar when his dad and i left each other but he would only do it out side in fornt of every one. and i know what you mean about beeing marreid to a solider i am married to a sailor.

I can't really offer advice,just know that you are not alone.
My step-daughter pees anywhere she wants to,whenever asked why all she says is because she had to,so then I ask why didn't you use the toilet and all she can say is, I had to go pee.
I am so frustrated I could rip my hair out. I could use advice on this matter to PLEASE....

A little about me:
I am a 31 year old mother of 2 my son is 5,my daughter just turned 7. My step-daughter just turned 5 and she is the one who pees everywhere. I also have 2 step-sons that are 13 and 14..

I have not expericened anything to this degree of a child not coping with strong emtions. You are right this is bad behavior and should not be tolerated to any degree. As far as your own children it needs to be explained that this is not how we behave. I am currently reading a book it is called "How to Behave So Your Preschooler Will, Too" this explaines about preschoolers and some of the things they expericen and the best way to deal with them. Always remember keep it positive when dealing with children and they will go far in this life. Happy reading and close the door to the bedroom all the doors ecept the bathroom if need be.

What is their situation. You didn't really give any information about them, and why they are staying with you. What is their life normally like? It seems like she is acting out for some reason. Maybe the move is traumatizing to her.