Hey guys - saw this last night but it was too late for me to post a good reply since I was dozing off on the recliner.
This is a tricky one since each dog has its own level of maturity when it comes to bladder control. It can be a combination of excitement and submissive behaviors. If she's housebroken and only does this on initial greetings then its more of a psychological issue to overcome where her brain gets so excited, it creates hormones and physical response automatically. A few things to consider:
1. I always ask my clients about how much water they give a puppy/adolescent dog. The general rule of thumb is the puppy or young dog should be able to hold it in based on months of age plus one - so for example if she's 6 months old = 7 hours. That being said, if shes drinking a lot on and off during the day she might not be able to control it yet.
2. If shes just letting it fly without squatting to pee, she doesn't even know shes doing it so be mindful of corrective actions on your part (i.e. yelling no, etc..) this could actually make it worse.
Try reducing the water a little bit. Then you need practice some random greetings where you ignore her initially, so that her excitement level stays low and then reduces the chances of excited pee response. You can try this every few hours since dogs have no concept of time, when you leave and come back it doesn't matter the duration they see it the same once you're out of sight for a while.
And while this sounds cliche, if she's an excited dog then you might need to add in a few extra play sessions to burn some energy and make her more tired (i know this is a catch 22) but this way when you greet her later she won't be as physically excited. I also remind my clients that dogs also get mentally excited too, so you could consider teaching her to stay laying down on her bed when you greet her. Or have her lay down at your feet rather than sit - since they can't pee as easily when lying down.
Hope that gives some ideas that could help.