I'm happy that you have asked me to assist you with your child and hope that you can benefit from my many years of helping parents like you.
First, let me reassure you that this is NOT cancer
Lymph nodes are distributed all over the body and are responsible for helping to concentrate white blood cells to areas of inflammation or infection. The fact that they have been there for so long is not worrisome at all and actually the main reason I say that this is not cancer.
Lymph nodes behind the ears are nearly always due to inflammation on the scalp and cradle cap is a common cause, as are bites, scrapes, cuts, etc. Once swollen they do NOT go away so don't hold your breath waiting for any of her nodes to go back down. In children, with all of the stimulation of the immune system from the multiple infections, cuts, bites, scrapes, etc they never really get the chance to shrink back down since they are little factories for helping to fight off these problems.
It is truly a rare child I examine at her age who does not have lymph nodes palpable in the groin and in the posterior and anterior cervical chains of the neck. I would be more concerned if I did not feel them as that would mean your child is overprotected from injuries, accidents, and common childhood infections!
Please let me know if you have any questions but again, you really don't need to worry about what is really normal adenopathy in a toddler.