My 4 year old daughter has big gums and small teeth. Should I be worried?

Probably not. Although there are some rare genetic disorders that cause this appearance, i would not worry. Tooth size and the position / appearance of the gum tissue is relative. Please see a pediatric dentist to assess the size and shape of the teeth and gums.
Maybe. It all depends on what you mean by "big gums". If the gums are big because your daughter is not brushing her teeth properly, the gums may be swollen because there is gingivitis. Also, if she is taking certain medications, these medications could cause overgrowth of her gums. See her dentist to determine if there is a problem which needs to be treated.
Yes. If something does not look right to you, then uyou must go to a professional. There are several reasons for large gums and they could be a symptom of a problem. Do not ignor the condition. It is right to see a dentist at age four. I recommend a pedodontist or children's dental specialist.