Dog psychology: someone will know this?

Sounds like she's feeling a bit insecure. Your friend might look into crate training.
Pups don't generally take well to being left to alone in the house. Giving them a "den" to stay in can help them to feel more secure, and aid in house-training (plus there's the added benefit that they can't destroy anything while they're in the crate). Our dogs benefitted greatly from it, and they still like napping in their crates, although we almost never shut the gates anymore.
Once the pup is feeling more secure in the house, the submissive peeing should stop as well.

I have bull terriers,absolutly the best most wonderful dogs in the world as far as im concerned but extremely energetic and very intelligent which turns into very destructive chewing behavior if they are bored or left on there own for too long.I kid you not but one of my males actualy chewed and ripped a hole through the side of my garden shed and i lost count on how many sweeping brushes weve gone through.
Spend a lot of time with them let them help you do the gardening,work on the car etc and make sure they have a mate to play with.
Male dogs peeing in the house makes sense but ive never had a female who pees in the house but a firm hand has to be used and disipline (i dont mean hitting although this works if you do it once or twice and there after use a stick more as a threat that an actual weapon)and dominance has to be asserted especially with big strong males who have the ability to physically overpower you.

I would suspect that your friend might be getting angry at her when he finds the pee spot. He might get tense, yell, rub her nose in it, hit her, etc. Her "guilty" look is her reacting to his anger rather than any sort of remorse. She's peeing to say, "You're big. I'm small." You can see this same behavior occasionally when dogs interact with other dogs.

I'm not so sure it's separation anxiety.  She might just be teething and feeling very bored.  I agree with RMS about crate training because a dog who destroys things might be a danger to herself if she gets into something she shouldn't or chokes on something she's tearing up.  However, she still might need a Nylabone which are hard to destroy and choke on if given the right size.

So responsible crate training and reserving anger/disappointment.  If he can't catch her in the act, there's no point in getting angry.  If he does catch her in the act, he just needs to startle her and redirect her to what she should be doing.  She doesn't know the rules and still needs to be taught what's ok and what's not.

One of my dogs used to chew on my shoes and the steps.  Every time I caught him, I would make a quick, sharp, loud sound to make him stop and then once he'd stopped, I would give him a cow hoof or plush toy which are both things he's allowed to put in his mouth and destroy.  It took a couple weeks of redirection, but he stopped chewing on things he wasn't allowed to.  This was all happening when he was VERY sensitive and fearful of any sort of correction, but he could cope with a startling noise and being given a cow hoof.  He now sees me as a "benevolent leader" rather than a tyrant, and if he makes a mistake, he knows I won't bully him.

I would recommend reading For the Love of a Dog by Dr. Patricia McConnell which is available in paperback and also on audiobook.  The title sounds a bit sissy, but it's a very well-researched book by a leading animal behaviorist.  It's all about human-dog communication and understanding dog behavior and psychology.  I also really like Victoria Stillwell's approach to training, and she has a show called "It's Me or the Dog".

Keep in mind 2 things when correcting a young pup. FIRST... they are wanting to please you and make their master happy so don't get mad at the little dog.. SECOND... the little dog is only a few months old and you are a lot smarter than the little young pup. I have found you must get the pups attention. Yelling at them does not help. If you smack them gently with a cardboard tube from a paper towel roll... it does not hurt them and it makes a "thunk" sound that gets their attention. Then say, "NO!!" firmly and loudly. My dog also had the "excited pee-ing" on the floor when i came home also. I found that if i gave the dog NO ATTENTION when i came home... dont even LOOK at the dog when you first come home. If you must you should even walk in the front door BACKWARDS so you dont look at the dog when you come in the door. That way, the dog learns to not get so EXCITED when you first come home. It will take several days or a couple weeks of this practice to see results. THEN a few minutes later when the dog settles down... then you can pet the dog and she will learn to not get so excited when you first come home. I have always found that when i have a problem with a dog... it is almost always something i am doing wrong... not something the dog is doing wrong. I suspect, the owner was coming home and petting the dog or scolding the dog as soon as he was coming in the door.... the little pup may not be mature enough to have good bladder control and the excitement is just too much. Remember, we are a hundred times smarter than a several month-old puppy.. so don't get angry at the pup. Any time you get a new pup you should expect to have problems and mishaps and potty messes for about 6 months to a year untill the dog finally learns what is expected of him. Try to take the dog outside every once in a while and say "GOOD DOG" when he messes in the right spot (outside) and pet him. After many times of smacking with the paper-towel tube... it is not necessary to ALWAYS smack the dog. Just the stern, "NO... BAD DOG!!!" lets the dog know you are NOT HAPPY with what he did.

A few things:


He has to establish dominance over the pup -- there are several non-violent ways to do this involving posture, voice and attitude.

Pay off GOOD behaviour.

Dogs have a LOT of energy. If you don't give them lots of playtime, especially when young they won't burn that energy off, and in boredom will wreck your stuff.

> pattern of destroying things while he's out
.  Canine separation anxiety. The dog is reacting to being alone. It's bored and uncomfortable with being alone.
 
> he finds her looking guilty and she pees on the floor.
.  Submissive peeing. She's telling him that she knows he is the alpha dog

.  Both are common in dogs and both are easily fixed. Google "dog training", "dog behavior", &c