I agree with chelleyrae something is upsetting this child , could you give us more information about her behavior, has she had any new happenings in her life, new day care/school, new sibling, change in Family ?
You mention that they think she is ADHD, but has she actually been tested and diagnosed? If she has a diagnosis, there are treatment plans available, and a psychologist will be able to help you with the plan. How are your daughters verbal skills? Is she able to clearly communicate her wants and needs to you? Or is she simply tantruming at being told no, which would simply be behavioral in nature. The first thing you need to do is look at the antecedent (causes) of her crying and throwing things. What is happening to make her upset?