I feel sorry for her. If she she was bossed around all her life by her older sister, her fear and atagonism to anyone who might try to do so again is obvious.
Also if she is 4ft 2 inch, almost everyone she meets including many children must be much taller than her and that is also intimidating.
My reaction to her would be endless sympathy and understanding. Constantly reassure her, but accept that the circumstances of her life must leave her constantly in fear of people who think her small height means that everyone else knows much better than she does what is good for her and that she has constantly to defie them.
Of course she has a chip on her shoulder, so would I in her circumstances.
Anger management!!! Help needed.