Extreme Tantrums

I agree with S.H. and Kiwimama -- I don't think you need to worry about anything being "wrong" with her. She sounds like a high-spirited and stubborn 3 year old. Some kids are definitely more work than others, but that doesn't mean there is anything wrong with them.

Limit sugar, it can't hurt. Meanwhile, really pick your battles, and remember her brain isn't formed yet.

(I just had a memory of my oldest son throwing a fit and rolling down the aisle of a restaurant. I'm sure the other customers loved it. But he was and is normal.)

I wouldn't worry too much that something is causing it yet. I mean limiting sugar is a great plan, but she might just be asserting herself. My daughter is almost 4 and super smart as well. Most of the time I can reason with her about everything, but some days oy! She went through a horrible phase a while back. One fit was so bad at my sister's house that I went to put her in the car to take her home and in my distracted hurry I locked my keys in the car with her strapped in the seat. It. was. terrible. Worked out okay in the end and she survived.
Maybe discuss before you go places that if her behavior is less than expected she will be going home for a nap without question. Also (i tried this with my daughter, which actually was kind of funny) keep a strait face and ask her before you leave, "what should mommy do if you are throwing a fit? what do you think should be your consequence?" Then if her answer is reasonable, try it if she throws a fit. If she sets her own consequences (with mom's input) she might be less apt to get so aggravated at times.

It could be her medication too....
not all allergy pills... react with a person the same way as the next person.
And she is a young child....

My Mom takes Zyrtec for example. but I hate that and the way it makes me feel. So I take Claritin.
Is the Singulair... per her Pediatrician???

Does your daughter NAP?
If not, overtired toddlers, get way fussy... and short tempered.... and cannot function....
my daughter is/was like that.

Does your daughter have snacks in addition to her meals? If not, maybe she needs too. I don't mean junk food. Just good healthy snacks. My daughter, if she is hungry and does not snack... she gets Hypoglycemic... and MOODY.... and therefore, she needs to snack, grazing throughout the day... or her blood sugar drops.

But, 3 year olds, are not easy.
Age stage.
They also have NO automatic 'coping-skills' for their moods/frustrations and have to be taught that. Problem solving....
Even some adults have no coping-skills for their stresses/frustrations...

all the best,
Susan

Because of the family connection to sensitivity, that could be a fruitful avenue to explore. Food allergies are common, and can have emotional symptoms. There are also many, many chemicals that are part of our everyday environment that can affect mood in children and adults. Most of these chemicals didn't even exist a few generations ago, so our bodies are not adapted to them.

A very large and well-controlled British study a couple of years ago confirmed that not only several common food colors (two of which are banned in the U.S.), but also the preservative sodium benzoate made hyper kids measurably more hyper. See a report here: http://www.consumerhealthreviews.com/articles/GeneralHeal...

There are also other sensitivities/allergies that make children physically or mentally uncomfortable and hard to please. She might be sending out signals for help, but have no real idea why, if she's just always at odds with her own body.

I have severe chemical sensitivities, and get both physical and emotional symptoms to exposures to perfumed toiletries, home cleaning products, fabric softeners and air "fresheners." (Many of these are just downright toxic.) In group testing situations, I have watched children go from contentedly coloring to bouncing off walls, screaming, crying, or being impossibly stubborn just minutes after having drops of some dilute solution squirted under their tongues.

It would be worth checking out. You can try sealing all suspicious products in plastic bags and using free and clear detergent, baking soda or vinegar for most cleaning for the next 2-3 weeks, and watch for any improvements. If reintroducing the products back into the home then results in worse behavior, you'll have a possible solution to work on.

I know this sounds like a lot of change, but it's really not that hard to try. Most of the household products and toiletries commonly used are really not needed, and they are expensive. We believe we need them because the advertising is so compelling. But I've used very little for cleaning in my home besides baking soda, white vinegar, borax, hydrogen peroxide, and scent-free detergent for over 20 years. My house always smells clean and pleasant – and visitors often remark that the atmosphere is "calming." I think their bodies are noticing the lack of toxins in the air.

A., I would get her checked by a good pediatrician.
Was her brother born recently, or have you had some other major change?

When my daughter was about that age(she is 7 now) her Dr put her on singular and thats exactly what she would do. She was like a crazy child! I took her off the singular.