おもしろい means generally funny, amusing or something like that. On the other hand かのじょ は おかしい can be interrupted both funny and weird. It all depends on contexts. Say "crazy" in English for example. You use it sometimes in a good way and sometimes in a bad way. Anyways as you said, おかしい is used less frequently than おもしろい when pointing to something funny, and we use the word in a negative way far often.

I think 面白い is funny, but おかしい means weird...ぜんぜん意味違うと思います。が、おかしいの漢字の書き方は可笑しい，字面的な意味はバカバカしいです。おかしい＝変　　変態はおかしいひと。

面白い can mean funny ha-ha or interesting. おかしい can mean funny ha-ha or funny-peculiar .