The dentist said my daughter's teeth are too crowded and some need pulling. She is only 12. What should we do?

Second opinion. If a dr. Of any sort is afraid of a 2nd opinion i would find another dr.We try to act in the best interest of our patient and if you are doubtful of a diagnosis or treatment get another opinion-it is and always should be about you and your health.
See Orthodontist. First, make sure you are seeing a university trained orthodontic specialist with at least a 2 year post dental-school residency, and who limits his practice entirely to orthodontics. If you are seeing an orthodontist, and his knowledge and experience tells him that your daughter needs extractions, go with it. About 30% of kids need extractions. If you are not sure, seek a 2nd opinion.
Records. What kind of records have been taken? Do both parents have crowding that couldn't be fixed with expansion? There may be too much crowding, but sometimes a doctor gets used to treating their patients a certain way (extractions) and that is what they are comfortable with. You can always get a second opinion.
2nd opinion. See another dentist--while there are reasons for starting things early in developing mouths, a second opinion to confirm the first will put your mind at ease.
Malocclusion. It is possible she has some retained primary teeth(baby teeth). If she has a crowding issue it would be best to have a consult with a orthodontist. He can evaluate which teeth need extraction anticipating future growth. Your dentist can recommend one to you.
Get a Second Opinion. Many mouths with crowded teeth can be expanded to allow room for all of the teeth. Extraction of teeth may lead to future tmd problems and a collapsed profile.
See an orthodontist. You need to have treatment coordinate with your general dentist and an orthodontist to take care of the crowding.
LIsten to the dentis. Serial extraction is a wonderful way to anticipate the future orthodontic problems that may arise from future tooth crowding.
Likely pull them. If she is very crowded, taking out some of the perm teeth will provide space for the other to be aligned more ideally. If you are concerned you could get a second opinion from another dentist or orthodontist. This is very common for children with crowded teeth.