I'm having better luck with my computer this morning. Here are a couple more links (Q&A on separation anxiety):
http://leerburg.com/separation.htm
http://leerburg.com/qa/qna_category.php?categoryid=39
I'm not sure if there is any overlap in the questions on these two pages.
Carolyn, I second Bob's advice on the travel trailer. You want Greta to come to think of it as her home away from home, so, hopefully, she will be fine there, as she is when you leave her at your home, but it will take time and it would be best if you could have access to the trailer and work with her a lot before you actually go on a trip. If you can keep the trailer at your house, this will be easier; not so much if it is in a storage facility.
Likewise, when you are visiting family and she must stay in their home, try to get plenty of opportunity to work with her before you have to leave her for any length of time. Practice leaving her for very short periods and coming right back, just as you probably did when you were teaching her to be alone in your own home. Add duration of time very gradually. I realize this is probably very inconvenient when you're in a situation of visiting with relatives, but whatever time you can spend on it will probably help.
Also, you may already be doing things like this, but it can't hurt to make it a point to work her on her general focus and obedience in many different locations. Take her to parks (I don't mean dog parks of course), stores that allow dogs, even just neighborhood sidewalks, and instead of just walking her around, do obedience training. I think this opens her world a bit and helps her to understand that she is to listen to you wherever she is, and that she is safe in all locations, even away from her familiar home.
I don't know if you ever found a training club in your area that you like, but if so, maybe you could utilize it for a little work on the SA. I know, at my club, there are multiple rooms, and I could leave the dog (in a crate) in one part of the building while I went somewhere else. I would practice doing this in small increments at first. Or, if there's another member who would help you out, you could get her used to staying in one room with a person other than yourself while you leave for a while. (This is one of the exercises in the AKC CGC test.)
So, bottom line, I think it might help to start doing a lot of things with her in many different locations other than your home, so she can become comfortable in all kinds of situations and know that she is always safe and that you will always return to her even if you are out of her sight for a while. It will take time, but, hopefully, you will start to see some improvement.