彼女は多忙のため来られなかった。

tbd

She couldn't come on account of being busy.

She couldn't come because she was busy.

彼は多忙を極めていたので、自分で行かないで息子を行かせた。

tbd

He was so busy that he sent his son instead of going himself.

彼は多忙だったが、それでも私たちを手伝いに来てくれた。

tbd

He was busy, and yet he came to help us.

読書をする暇がないほど多忙な人はいない。

tbd

No one is so busy that they can't find time to read.

Nobody is so busy that they cannot find time to read.

多忙な生活を送る。

tbd

I lead a busy life.

たとえ多忙でも彼は来るだろう。

tbd

Even if he is busy, he will come.