S.H.
The "smartness" of a child, does not mean they are equally "emotionally" smart....
for a child of any level of ability... it is, to me, really important to develop the "whole" child... their level of emotions/coping abilities/self-esteem/social skills are real paramount.... in the LONG term and their success as an individual in making friends, socializing, being pleasant, understanding others, empathy, charity, etc.
She is so young... and at this age, their emotions are NOT even fully developed yet. So, perhaps, instead of focusing on how "smart" she is... try nurturing other aspects of her.... ie: how to communicate feelings, how to articulate it, how to cope with 'mad or happy' feelings, and that she is a "team" in the family.
THIS is what we did with my daughter, who is very wise beyond her years, and tends to be more articulate for her age. Her Teachers and others have always told us this. So now, at 6 years old, she is very capable of KNOWING how to express her feelings/thoughts/ideas (whether positive or negative), she can adeptly DISCERN good/bad situations and problems and trouble-shoot it wisely, she has a great self-esteem and values her self, we always taught her to "be yourself" but to give thought to others. Over the years, with learning positive "coping skills" from us, and that NO ONE is exempt from being above anyone else, she has really become a well-rounded little girl. She even teaches US a thing or two.
Many times, a child's "smartness" overshadows their actual "maturity" emotionally. So, instead of over-looking this aspect, work on it. THIS is what makes or breaks a person... in the long term. ie: we have a friend with a 'gifted' child and he goes to a special school for gifted children. BUT...over the years, I have seen how he is the most noxious little child I have seen.... spoiled, selfish, gives no care to how others feel, he has a sense of "entitlement" and that he is "smarter" than everyone else. He lacks social skills and most kids do not "like" him. Then he wonders why he has no friends, besides adults. And, he has no self-identity... just parrots what his parents have been telling him all these years... that he is SO SMART... and he lacks any "original" sense of self.
The thing is, no matter how "smart" a child... friends and feelings and the ability to fit in... will be important to them. Long term. You do not want them to feel marginalized or like an outsider amongst even "normal" kids. But, they must be allowed to go at their own pace.... and have the ability to RESPECT ALL KINDS OF PEOPLE... not just "smart" people. And, how to build empathy....
Again, your daughter is so young, and this is the "terrible two's." Even if she were normal intelligence, she'd have frustrations/tantrums/and a bad temper. So, like ANY child... work on the INNER child... the WHOLE child.
Any child can be hard to deal with.... smart or not.
"Success" & "happiness" for a child... will mean, especially in the teen years, how many friends they have, WHO they are, how they fit-in, how they manage their difficulties and emotions, how they can excel academically AND socially... how everyone "views" them, how their parents accept/negate their own ideas and problems, and how well they can communicate AND "relate" to others.... etc.
Build a "FOUNDATION" under your child.... not just academics and how "smart" she is. Give her wings to soar with... for the "whole" child and the little young lady she will "become." And, BOTH Mom and Dad influences, will color her world view... a Dad is just as important in "shaping" a little young girl too.
All the best,
Susan