Before I say anything else, I FEEL YOUR PAIN! Shortly after I adopted my own adorable little Cocker puppy, I too found myself dealing with the worst separation anxiety EVER. You can find a link to my forum post about it here: http://www.zimfamilycockers.com/Forums/ ... =35&t=5333
Here's a direct quote from that post:
As soon as he's placed in his puppy room, he begins YELPING, SCREAMING, BARKING, GROWLING...anything to get out. I don't want to give him attention and let him out, because I think it will only encourage his whining...but he carries on LOUDLY for ages...I've read other forum posts that said he should calm down after 5-10 minutes of whining...but we're talking this pup goes on for an HOUR.
I share this simply to say, it DOES get better. Oliver is nearly four now and thankfully in a much healthier spot.
The best advice I can provide is to gradually build up the time you leave her alone. Remember, she's still a baby. Try to give her two minutes of alone time, and then return and act completely normal. You want her to understand that your absences aren't permanent, and causing a big scene whenever you come find her can make her believe she SHOULD be panicked when you're apart.
As for the roughhousing, again, she's a baby. How old was she when she was taken from her litter mates? A puppy should never leave Mom and her siblings before eight weeks, and many breeders prefer to keep them a few weeks longer yet, simply to teach them how to play nicely. We're well past that point now, so focus on diverting her attention with a fun toy if she tries to get mouthy. She'll be teething for a bit and probably wants something to chomp on.
If she DOES bite you and growl, you need to put a stop to it and show her that her behavior ends play time. My favorite tip is to yelp LOUDLY if she makes contact with you—the idea is to show her she caused pain, much like another dog would make a sharp yelping sound. Turn your back and immediately stop playing or interacting with her. She'll get the idea—roughhouse play = no play at all.
Good luck! This is the time you get to really invest into her, so that you'll enjoy a happy, healthy adult dog down the road. Make sure she's getting plenty of socialization, and consider puppy kindergarten classes if you're not already doing so. These can be incredibly beneficial, as they'll equip you with some simple tools for handling her, while also teaching her how to appropriately interact with other dogs.