It happened again :(

Aww, poor little girl and poor you too. Maybe it was just too much stimulation for her today with the vacuum and the new people - I'd definitely let her have some 'safety' places she can hide, and a lot of cats do get upset with new people coming over and hide - I have friends with 12 year old cats who continue to hide everytime someone comes over - they may come out after a few hours, but mostly visitors never see them. The worst thing, for them, is when people try to get them to come out - we've all learned just to let them be. My own boy is bold and lovey dovey with me at home, and can warm up to people once they've been there for a few hours and have let him alone - but honestly, he also gets stressed with too much attention and too strange voices. And he's 7 years old.

Cats love, love, love routine, and Piper is still pretty new to your home - she's just starting to realize that it's her home and she still has memories of the shelter and being moved place to place, and from person to person, I'd bet. She might have thought the new people were there to take her away, and she got scared of that.

Maybe with Piper just keep doing what you've been doing - let her adjust on her own time, and when you have time, just sit and read or talk to her quietly, without staring at her, and let her come to you. And praise her when she uses the box, and try (and I know it's hard) not to stress when she has an accident - believe me, she can pick up on the tension you're feeling and she probably just doesn't know what's wrong with mommy and daddy, and that makes her tense too - and her tummy gets upset and maybe she just can't get to the box fast enough when the urge to poo hits her.

I've been there with my boy - I know how hard it is to be calm, no matter how you love them, when you can't figure out how to make it all better. But try to give yourself and chance, and remind yourself that Piper isn't acting out like a bad girl, but is trying to communicate as best she can that's something is not quite right with her world.

But don't feel bad if you end up finding putting her into her room is what works best for her when new things are happening - it could be for her that having a safe little haven is really best for her now.

PS - my boy cat is my llap cat and cuddler (and we've gone through litter box issues); my girl car loves me and follows me - but not once in four years has she sat in my lap, she hates being picked up, and she cries so much in the car that I'm practically crying by time we get to the vet. Cats are all so different - but I think Piper loves you, but still needs time to feel really secure and relaxed and 'knows' she's in her forever home with your familiy.

I think putting Piper in her room when you vacuum, have people over, etc. is a good idea. Three of my four cats are terrified of the vacuum, and two of my four cats are afraid of visitors. The two who are afraid of people will even hide in the closet in their room, for additional safety (even if they're in their safe room and the door is closed).

I give them extra treats and toys when I put them all in one room, and I think they don't mind a whole lot. They usually try to get as far from the vacuum as possible, and will put themselves in the bedroom anyway.

Actually, putting her in a separate room when people come over is the best thing you can do for her. Cats need to have a safe place. If she has a place where she knows that no strangers can get at her she'll be much happier. Once they're gone, just open the door and let her come out when she feels like it. Forcing her to share space with strangers will just traumatize her more.

I have one cat who is terrified of all people except me. If I don't close the bedroom door when she goes there to hide she'll get into the deepest darkest corner of the closet. She won't come out for at least half an hour after the other people have left.

Oh my! She sounds so much like my Callie used to be. The vet finally diagnosed her with stress induced fecal incontinence. Basically, when she's really stressed out, she'll poop in inappropriate places. This happened a couple of times when I first got her and would take her with me in the carrier and then it didn't happen until about 7 years later when we moved and she pooped a couple of times in the living room because she was overwhelmed with her new living space. Aging, becoming more comfortable with us and her home, and using Feliway have helped her. Also, keeping her on a routine has helped. Lastly, we used to put her in a room and close the door when we vacuumed and/or had company over. Again, she's become more confident and we no longer do this. When we did, though, it helped tremendously.

When you vacuum or do anything out of the ordinary, place her in a room with food, water, litterbox, and Feliway diffuser to see if that helps her. Also, provide her a little "safe place" like a box turned upside down with a hole cut in the end for her to "hide" in when you put her in the room.

Only one thing to add to the excellent advice:

Don't comfort her when she gets scared over visitors or vacuum cleaners. That only reinforces to her that it is something to be scared of. Just let her hide out in her room, and treat it all as matter of factly as possible.

Rescue Remedy is a good safe herbal supplement for stress in cats.

Along with some of the other posters here I too have a cat who gets stressed when strangers are in the house. She also vanishes as soon as she sees the vacuum cleaner. A vacuum cleaner must be terrifying for a cat! I agree that you should leave her in a room to avoid stressful situations until she is more settled. Everytime we have visitors Ripley runs upstairs and hides, I don't let anyone go upstairs (luckily we have a downstairs bathroom!) and she will come downstairs after they have left in her own time.
She used to urinate outside her litter box when strange people were in the house (often frustratingly on my bed) but now she knows she has a 'safe place' this has stopped.

Just curious - hope things are going ok?