Sometimes, it seems like she is completely spaced-out.
It's as though her brain has temporarily stopped working and she stares off into space.
She doesn't reply even if I ask her something.
ご質問ありがとうございます。
"Sometimes, it seems like she is completely spaced-out."=「時々、彼女は完全に思考停止しているようです。」
"It's as though her brain has temporarily stopped working"=「まるで彼女の頭が働かなくなったかのようです」
"and she stares off into space."=「そしてどこかをボーっと見ます。」
"She doesn't reply even if I ask her something."=「何か私が彼女に聞いても、答えません。」
ご参考までに。