My 2 yr daughters foot( ankle) is swollen on one side. it has happened before also. what could it be? an insect bite or something to do with blood?

Unknown: What was the cause before and how was it treated? Could be bite, could be something with blood. Possible injury. I would bring her to the doctor for evaluation and treatment.

Get it checked: There's no way to diagnose this issue with the limited information provided. Recurrent ankle swelling in a child isn't normal. Have a podiatrist, preferably one who sees children regularly, evaluate her. This could be an injury, congenital issue or early inflammatory arthritis, among many possible diagnoses.