I have an unhappy 9 year old daughter, too. I am completely available for her. I work while she is at school, get her ready and drop her off, pick her up from school, stay home all afternoon/evenings, weekends, etc. I pretty much cater to her all day and she is still unhappy. She has these horrible outbursts where she stamps her foot, tries to push me down, glares at me, tells me I'm mean and not pretty enough, etc. This is usually when I am trying to be helpful in the most careful, nicest way I know how, when she's asked me for help! So being with your daughter more might not be the answer. I never yell at her and have never spanked her, I try to talk out what happened after she's done exploding, but it still happens, sometimes three or four times a week. I'm tired. When she gets going, nothing will snap her out of it until she's done. It can last an hour! I wish I could walk out of the house and keep going.
One thing to weigh is the degree to which the family is under stress due to the collection of your schedules. If you find yourself yelling, it is a symptom of your own stress and it may be contributing to the unhappiness your daughter is displaying. It may be that you and your husband are not sufficiently available to the children. They are young and require a lot of attention, and some children are better able to 'roll with the punches' than others. It would be prudent to have your daughter evaluated by a pediatric mental health clinician to gain a perspective on the 'source' or nature of her unhappiness. The sort of complaining and dissatisfaction you are describing is not typical of a child of nine.