What are we doing wrong?

[Charbeaner]

My daughter loves her hamsters more than anything and she takes really good care of them. Up until now our all of our hamsters have always lived about 2 years but we’ve had some really bad luck lately. Last summer she adopted a hamster who was 6 weeks old. We got a massive second hand cage and sanitized it with vinegar and lots of scrubbing. We added a bunch of wood toys, we gave her oxbow hamster food and mealworms plus some hamster safe treats (fruits and veggies etc) and clean water daily. After only 4-5 months she died very suddenly after being 100% normal the day before. We thought she must have been sick so we waited a bit, resanitized the cage, and got another hamster when my daughter was ready. He died after 3-4 months. My daughter was beside herself. We went to the pet store and chatted with them for over an hour (they are very knowledgeable at this store) and they said it sounded like we were doing everything right. We reluctantly decided to try again. We sanitized the cage, got new food and brought home another hamster. She died after only 2 months. We have no idea what we are doing wrong and my daughter is inconsolable. Could it be the cage? Or the toys? We are likely not going to get another one as it’s too much heartbreak and we don’t know what’s going on. Any ideas or suggestions? We may get rid of the supplies but I don’t want to pass on anything that could be harmful.