It's obvious you're giving her preferential treatment over me.
この場合、次のような言い方ができますよ。
ーYou are clearly treating her differently than me.
「先生は明らかに私と彼女の扱いが違います」
to treat someone differently「人を違うように扱う」
clearly「明らかに」
ーIt's obvious you're giving her preferential treatment over me.
「先生が私より彼女を特別扱いしているのは明らかです」
preferential treatment「特別扱い・優遇」
ご参考まで!