Blood draw for 2 year old check up? Question for moms

I have a question for all you mamas. I took my daughter in for a 2 1/2 year old check up. I knew that she had to get a lead test done because they forgot to do it at her 2 year old check up. Well when we got to the Dr office they told me she was due for another test too. I can't remember what it was called but they said it was to check her iron levels and check for anemia. I was under the impression it was going to be a little finger prick like they did the last time she had to have her iron levels checked at 1 year. Well they ended up doing an actual blood draw. They took 3 viles of blood. I don't understand this. Why was this necessary? I asked if they could just prick her finger but they said that would be more painful. I don't believe that at all. I have had both done and a blood draw needle is way bigger and more painful. I wish I would have refused it because my daughter is now terrified of the Dr. Office. She cried so hard.

I guess my question is..how do I figure out what procedures are "recommended" and what are "mandatory"? And who has had this procedure done to their child?

I am a full believer of vaccinations. Im not anti needles or anything. I'm just wondering if putting her through that was actually necessary. I am feeling like a terrible mom because I didn't have the back bone to stand up for my daughter and just ask if this was optional. I hate that I don't ask questions and just do what ever they tell me to because they are medical staff.