Read the dialogue below carefully and answer the question!

Farel : Hello, this is Farel speaking.
Olive : Hi, Farel! It's me, Olive. I didn't see you at school today. What happened?
Farel : My grandma fell sick. We had to take her to the hospital.
Olive : Oh, no. I'm so sorry to hear that. Wish her speedy recovery!
Farel : Thank you! The doctor told us she'll be out in two days.

Olive said, "I'm so sorry to hear that." What does this expression mean?