She's not grooming herself as she did before, and tends to get a little mouthy. We get along fairly well without her mother and the two children from her present relationship -- a two-year-old and a six-month-old. Could this be a good part of the problem?
Normally my granddaughter is a loving, highly intelligent, well-behaved (in public) child. This behavior has us flummoxed. Her brother is horribly jealous of her, and tends to treat her badly at times.
Your granddaughter is exhibiting some extreme attention-seeking behaviors, and may be testing to see if you really love her. Be consistent with your rules and expectations, as well as with your consequences for breaking rules. Also be sure to give her positive attention when she is behaving appropriately. Children see our limits, consequences, and praise as evidence of our love for them.
Part of what you are seeing may be the ordinary steps to independence we see in most seven-year-olds. At this age they are realizing more and more that they are in control of their actions, and she may be testing the limits a bit.
Does your granddaughter have much contact with her mom and the two younger children? Her immature behaviors could be an attempt to compete with the little ones for attention.
Reassure her that although you do not like her behavior at times, you will always love her and take care of her. Make sure, too, that there are consequences for her older brother when he mistreats her. Both of them may be dealing with feelings of rejection by their mom and they both need reassurance that they are loved.
If these behaviors continue, the school counselor or your pediatrician can refer you to a therapist for additional help.