How old is she? I was maybe 8 at the time. I was not in Beijing. Even I knew what was happening, the event was broadcasted on TV at the time. It was probably heavily censored, but I knew demonstrations etc were going on in Beijing at the time.
There's a big difference. In the US we've been educated about atrocities against natives since youth. We learned about the Trail of Tears. You know about the Jallianwala Bagh massacre if you've watched Gandhi, a piece of Western film and entertainment.
That's incredibly different from the state overwriting or hiding history.
What are you talking about? Americans definitely care about what in the past, but you can't change things that happen in the past. The country, unlike China, is very open about the cracks in its core. There's a huge monument to MLK on the mall in DC. Can you say as much about Tienanmen Square?
Regardless wether people care about those things(a lot don't), it's part of our education and media. I think the claim is Chinese history classes in china and their media are a bit more rose colored than ours, which is why people don't know about tiananmen square.