「however」は文頭・文中・文末いずれも使用可能で、書くときは「コンマ(,)」で区切ります。 下記の例文は全て同じ内容ですが、「however」の位置が違います。 どれも文法的に正しいです。

She didn't want to go, however, she went. She didn't want to go. However, she went. She didn't want to go. She went, however. She didn't want to go. She, however, went.