i'm not sure if this counts as seperation anxiety, but i'm pretty sure treating it as such can't really do any harm and will probaby help with the issue. for that you can google seperation anxiety on more info, but here's the basics:
--- crate train! now i dont know how old penny is or if she has been crate trained, but the general idea is that the dog will (if properly crate trained) see the crate as its den. this means that the dog feel more secure in it, than being left out. i am not sure if this is something you want to consider. and there arent any guarantees, since theres also dogs out there that just NEVER take to the crate and do worse in it than when left out. but i wanted to throw it in there nevertheless. if you want more info, i'd be glad to give you some pointers.
--- make leaving and coming back LOW KEY!! this means no good byes, no high energy games just before leaving (just gets the dog in a state of high excitement, instead of a calm mind set), etc. just ignore penny for a bit before you are leaving and while you are preparing to leave. if she jumps, barks, nips: ignore! this will teach her two things. A) no matter how much she throws a fit, it wont change a thing about you leaving. B) you leaving really isnt that big a deal!
same goes for when you come back. when you come back home, no matter how long it has been, just ignore her until she is more calm. that as well will give her the idea that you leaving and coming back, really isnt anything to make a big deal of!
--- give her something to occupy her mind with, while you are gone. this will take her mind of the whole "leaving" thing, plus it gives her something to look forward to, for when you leave. the kong is a GREAT idea. in fact in my house, the only time the dogs will ever get to see a king, is when i leave the house! usually they dont even look up to check on me, when i leave... too busy with that yummy kong!
hope these things help a bit...