violetsareblue if this is a one-off incident of innocent questions I personally would not be too bothered.
If you are bothered, or more to the point your dd is, then I’d say it is a question of is it appropriate. Innocent of questions are usually not a problem, but if the questions are not so innocent or if they are repeated after an answer has been given that is more serious (to me).
It is just horrible when a child is upset.
I would use this as a time to cover all their points in answers with your dd so she knows what to say if this comes up again.
EG ...Why she didn't have "small eyes"? Does this mean they think she has big eyes? Do you think she has, if she has, that's fine as we all have different shaped and sized eyes.
Why she didn't look Asian even though her father is half Asian Simple maths says if you are a quarter Asian you will not look very Asian, but you may have dark hair etc like your dad.
Comments or even compliments about ... "smart Asians" are fine as long as it does not lead to negative comments, once people start generalising about some people being good at things because of race or ethnicity they could go on to say negative things by the same token, surely kids are good at stuff, or not, due to a whole host of reasons!
Personally, as a mum to an adopted son who does not look like me I would find ...asking her if she was adopted because she doesn't look like DH or I intrusive. If a child is adopted they may not wish to discuss it with kids in their class. Clearly your dd is not adopted so she could very quickly silence this speculation with 'I am not adopted' and the fact she is asking about it may mean these questions have made her feel a little insecure. I would reassure her of the reality of her situation.
Once your dd has her answers straight for if this happens again and she is reassured I would ask her if she would want to complain at all about this. My guess is she may well say no, so personally I would not take it any further at this stage. However, I personally would prepare dd that if the same children, or others, ask these questions again she is very clear with her answers and say that she does not want to discuss this. If it were me I would say to my kids, you are who you are, your parents are who they are and you don't feel the need to talk about it all a lot, you could say, let's go and do something more interesting.
If the questions do continue I would complain by letter (getting my thoughts clearly down in a letter helps me and also, often, conversations with teachers are in open classrooms overheard by whoever is passing!).
Generally, for me, I only complain to school if DD is happy for me to do so.
I had a recent problem with dd at school, not related to race or adoption (she is not adopted), and I wrote to school. The question might come up in my dd’s case 'is this really bullying or just some unpleasant behaviour?'. In your case it may come up is this really racism or just some unpleasant behaviour?' Personally, I would rather not debate if it is bullying or racism or just unpleasant behaviour, kids are not at school to be upset. They are at school to learn and if it upsetting your child I would try and put a stop to it but only if it continues and continues to be upsetting.
Good luck.