Your question brings up an important concept regarding how to determine toxicity.
Your daughter is probably using a very small amount of hydrogen peroxide to kill bacteria and keep her ear holes from getting infected. So the choice here is to use hydrogen peroxide or some other bacteria-killer or risk infection, which would cause a greater problem.
It's the nature of hydrogen peroxide to damage bacteria--that's why we use it. To kill one thing bacteria to preserve another ears.
Remember that whether or not an exposure is toxic to you is based on the inherent strength and toxicity of the substance, frequency of exposure, amount of exposure, method of exposure, and one's individual tolerance for the substance. Hydrogen peroxide is known to be safe and effective in small amounts for a variety of health uses. We don't know how much was used in this experiment and the length of exposure required to cause the cell damage. Enough table salt--which is vital to our health--can cause cell damage enough that it was traditionally used as a preservative to prevent food from spoiling.
I'm not worried about your daughter using hydrogen peroxide on her ear holes.