Peeing when excited......

I always put little ones in their crates BEFORE guests arrive, and honestly by the time folks are coming to look at foster pups, never before 10 weeks, they have been taught that jumping up isn't allowed.  Licking I don't care about since they outgrow that soon enough, but jumping earns an "eh eh, OFF".
 
I also tell guests before allowing them access to the pups that they WILL pee if the don't ignore them until they are calm, and if the PUP pees the GUEST gets to clean it up.  I mean it too.  When I ask my guests to follow a direction that is in everyones best interest, I don't hesitate to hand THEM the paper towels if they refuse to comply.  I can be a bit of a hard a$$ about some things! []

You also have to be aware of how people are coming up to her to pet her.  Towering over them and reaching a hand above their head is scary for a pup.  Try crouching down next to her and reach to pet with your hand palm up.  And pet her first on her chest, neck, front legs.  This should help.  And I agree with glenmar about the visitors.  If they don't listen when you tell them to stop, let them clean up the mess.   Good luck!

coco only does it when she needs to pee anyways... so a full bladder and a new guest = a wet surprise.
 
so when someone comes over, i make sure she goes potty before meeting the new guest.

Make sure the dog is in a crate or behind a dog gate before you let the guests in.  This gives you chance to explain that if they make a big fuss of her, she will wet herself and you'd rather they let her be so you didn't have the mess.  If you have a feeling they will ignore you, (young children might find it difficult for instance) then she can be left in peace and quiet with a bone, chew or well stuffed Kong for the duration of the visit so that the habit is not reinforced some more.  If the guests are understanding and cooperative you can wait until the initial excitement has dissipated before letting the dog come in - wait for her to be calm.  She is less likely to become overwhelmed and pee and she is going to be more open to learning correct meet and greet etiquette (four on the floor and/or Sit, not bodyslamming).  If she appears to be getting worked up, put her back in the crate or behind the dog gate to calm down.  It's not a punishment - it's a chance to cool off.

Making her being calm is the right step, you have to check if when you tell her to sit she is paying attention to you and taking you seriously or if she's still focused on the person, she can have her butt glued to the floor but that not always means she is calm

If the person that is going to meet your dog comes whit an excited attitude "because your dog is so cute" then that is like adding wood to the fire, the people also has to be calm at the moment of meeting your dog and i agree with making them cleaning the mess if they didnt respect what you told them

Making them clean the mess wouldn't really help the fact that the dog has repeated the behaviour and it's become that little bit more ingrained.  Satisfying if they DO screw up I'll grant you but better to prevent it if you can.

Before guests come over, I would first take the dog out and run her around a lot. A tired dog is a good dog ... and exercise in the yard encourages pups to pee.
Secondly, 10 weeks is really young. I've seen lots of pups not have great bladder control at this age.
Thirdly, I would teach some deference exercises so your pup can learn self control. For example, have her in a sit. Have someone go towards her. If she remains calm, praise and person comes closer. If she's excited, you turn and walk away and then put her in a sit again.
When she learns self-control and her attention span gets better, you can use sit-stays and down-stays to encourage calmness. Basically the dog equates calm/sit/down with being able to meet someone, and excited/jump/pee with walking away from the situation.
(If this doesn't make sense, please let me know.)