The key is patience. This is a phase, and a pretty long one- not just a correctable behavior. It will not go away immediately. It won't go away for months. GSD pups are lovingly called "landsharks". At this age, all you can do is be consistent with the redirecting, and eventually she will outgrow it. And when you get frustrated (I look back on the landsharking with fond memories, but at the time it was miserable), just take a break, take a breath, and remember she is a baby and puppies explore their worlds with their mouths- including how far they can push the boundaries. She's not trying to be "naughty". Just keep up the good work with the redirecting and teaching bite inhibition, and it will get better! There are some great links stickied in the puppy section that should help you out.
One thing I noticed- when you say you walk into a room and being happy once you get back, you may be amping her up even more to play and be excited. When you come back, be calm and quiet instead. If she starts getting too ramped up, put her in her crate for a bit. Not as a time out, just a sort of "reset" so she can calm down and you can get a breather.
Curbing boredom is also key in keeping them from getting too ramped up. It's hard for them to get rigorous exercise at this age, but lots of running around on grass, etc is good. The BEST thing, though, is mental exercise. How much do you train with her? Obedience work is key, but at this age, keep it short, light, and fun- make it a game. Teach her tricks, etc. It's great that you guys play with her so much-- now make her THINK for your attention