It may just be her nature... some dogs are naturally very nervous or over excited.
I don't think it sounds like a medical problem.
Weims and Labs are both very energetic hunting/retrieving breeds.
Have you tried separation anxiety training?
I will post my method below for what I do to resolve the problem, have a read and see if you think it would benefit you in your situation.
Does your dog cry when you leave the room? Urinate only when you leave the house?
These are a few signs that your dog may be suffering from Separation Anxiety.
Some dogs do not like being left alone and some will think you are leaving them permanently and not coming back. Here are a few tips to help fix this problem.
When you leave, no matter how long for always have fresh water available. Toys are also a wonderful training tool as it will keep the dog distracted, I use kong toys stuffed with yummy food as a cure for boredom, having special toys or treats that the dog gets only when you go out are also a wonderful idea.
When training my own dogs for separation anxiety I first distract my dogs with their favourite toy and then exit my house through the front door.
I only leave for a minute or two, just long enough so that the dog does not bark or cry.
I then re-enter the house and give them praise for not crying.
Next time I go out I leave for a few more minutes, again only entering the house if the dog is not crying and giving praise.
Increase the amount of time you leave for and always come back before the dog starts crying (you will learn how long that threshold is pretty quickly)
This teaches the dog that you are going to come back and they are not being left alone forever.
Another technique is to not "baby" the dog.
Some dogs become overly attached to their owner and don't even like their owner being out of their line of sight, in this case the training needs to begin before you start going out
Start paying less attention to the dog, when he pushes for attention, don't give it to him
If he wants to be petted, make him wait.
As harsh as it sounds it is the only way to get the dog to start becoming less dependent on you.
After you have trained the dog to be less clingy you can move onto things like leaving the dog in the living room while you have a shower, or leaving him inside while you are out hanging up washing on the clothesline.
Another thing you may want to consider is crate training her when you leave, a lot of dogs fell more secure and safe in a crate when you are not home.
Some people say that crating dogs is cruel but from personal experience the dogs don't mind at all, in fact, mine love their crates.
Let me know if you would like some information about crate training