hi, sorry to hear this about your friend. if you can meet her face to face, then you should use phrases like "I am sorry this has happened to you" and "I am here for you whenever you need me", and try to make her happy give her meaningful gifts and talk about other topics, make jokes, just don't make her health the main topic of discussion. if you can't meet her face to face then you can send the gift and message her the same.

I feel so sorry about your friend. in this situation you should talk to your friend in person. She might be hoping someone to be with her who can listen to her. whether it's early stage or last stage you always have to make positive conversation and positive hope. we all live with some hope. I'm never been through such situation , what came to my mind I shared. And She's very lucky to have friend like you who's thinking about her in her worst days. Good luck friend.