My daughter is on amoxicillin, 9mL twice a day for an ear infection. She is 3 1/2. How many hours should be between each dose? Thanks for your help!

8-14. Just let the dosing fit into your regular schedule. Like getting her up and getting her to bed.You are less likely to miss a dose if it is paired with something you normally do anyway.
It doesn't matter. When using amoxicillin for treating an ear infection, it doesn't matter much about the hours... meaning for "twice a day", a patient can take the medicine after waking up in the morning and again at bedtime. If taking it "three times a day", a patient can take it after waking up in the morning, middle of the day halfway between the first dose and bedtime, and the final third dose at bedtime.