My ADHD daughter, when she was younger, was very polarized in her thinking . . . but it does improve with time and effort.
http://www.strongbonds.jss.org.au/workers/youngpeople/thinking.html
See above for a link to a handout for black and white thinking in children: it has strategies you may want to try, an explanation about B&W thinking in children, and ways to cope.
Also, ADHD brains take longer to mature . . . she wont’ be at the same rate as her peers but she will get there (see below for article).
Lastly, “Raising Your Spirited Child” Mary Sheedy Kurcinka is a great source for words of encouragement to use with your child — especially a child that may feel emotions more intently.
One step at a time on the parenting road.