Border Collie being overly protective / aggressive

Hi,
I have a very sweet border collie but lately I have been having trouble with something. She has become very protective about her stuff or place, so whenever I go picknicking or camping, and another dog walks by (sometimes she does this with humans as well) and comes bit too close, she becomes aggressive towards the other dog guarding her 'people' and stuff.
I do not know how to handle or prevent this from happening, she is actually really good with other dogs unless they come into her zone or try to drink from her bowl or steal her ball.
She was also raised as the only dog in the family so she never really learned to share.
Thanks for the help!