Behavior problems with a lab/pit combo ...

Question
Hi ... we adopted Sydney about a year-and-a-half ago.  She's part lab/pit, and according to the paperwork, about 5 years old.
  She's been showing more signs of aggression lately, mostly towards our 11-year-old daughter whom she's snapped at on a number of occasions.  More recently, about two weeks ago, she badly bit our older daughter (19) whom she thought was going to take away a rawhide bone.  We've since discovered that rawhide bones make her act very aggressive, so have gotten rid of them, but she snapped at our younger daughter again today when she was whispering to me, being driven by jealousy as far as we can tell (other times she's snapped at our daughter has been when she's hugging my wife).
  As you can see, it's getting discouraging and we need to find a trainer or someone who can help us stop this behavior before Sydney goes back to the pound.  Do you have any ideas on how to control aggressiveness in older dogs?  Any help would be greatly appreciated, as we'd hate to have to get rid of her, but are also concerned about our daughter's safety

Answer
I have more  experience starting dogs out right, than fixing older ones.  I don't see her being part Pit Bull as the problem, but expect less tolerance from the rest of society because of it.  Dogs can still learn at that age, but it is difficult.  Three is a common time for problems to start.  Much of a dog's personality is determined by genetics and early socialization.  The personality is not fully formed until about 3 years old.  Since nobody in the family is giving her the leadership she needs, she has decided she is top dog and can control the rest of you.  As top dog, she feels she has the right to be aggressive and snarl at you and your offspring.  

Spay her if not already.  It is not a cure all, but can reduce aggressive and dominant behaviors.  Obedience train her. The dogs see all the
people and dogs in the household as a pack with each having their own rank in
the pack and a top dog.  Life is much easier if the 2 legged pack members
outrank the 4 legged ones.  You can learn to play the role of top dog by
reading some books or going to a good obedience class. A good obedience class
or book is about you being top dog, not about rewarding standard commands with
a treat. Start at http://www.dogsbestfriend.com/

Eye contact is very important.  Meet any aggressive behavior with a firm ''Bad dog!'', and make eye contact.  Maintain it until she looks away.  If that provokes more aggression, try the squirt bottle.  Fill it with water and a little vinegar or lemon juice.  Give it a squirt in the face.  Dogs hate that.

If you could find a rescue near you, they might be more help than I am. They take dogs that lost their home into a foster home to be retrained as necessary and placed in the right home for them.  You may find a rescue near you starting at http://www.akc.org/breeds/rescue.cfm  They are private and work very differently from a shelter.  I am not sure many trainers are much better with problem dogs than I am.