Okay, so basically it sounds like it's really only a matter of "object guarding" which is quite common in dogs and can be treated.
You have a done a
great job with teaching "drop it" and with working on her being comfortable when you approach her when she has most objects. She just needs more work on these.
Here is a link to an excellent article on how to deal with this:
http://www.clickersolutions.com/arti...ex.htm#problem
If you don't get the help there that you want, you might consider either calling your trainer for guidance or buying the book
MINE: A Practical Guide to Handling Resource Guarding by Jean Donaldson (available from Amazon).
As you said, she IS a great dog! She just has this one issue which can be worked on!
If you have any questions, let me know!