Honestly, everything that isn't a (battle) shounen should be great. The most important thing is to firmly establish that anime is a "medium" and not a "genre". And since almost every outsider thinks every anime is a battle shounen, it's important to correct that misconception early on.

AnoHana would be my recommendation. It's short for a series, it doesn't take any Japanese cultural knowledge to enjoy it, and the themes are universal regardless of personal background, age or gender.