Maybe you can't be there physically, but you can offer spiritual and moral support by being available.
If your friend needs to talk, then listen.
If she is afraid, encourage her.
If she is sad, reassure her.
If she's angry, be compassionate.
If her spirit weakens, ask God for help.
If she's irrational, be patient.
And if it's her time to go, be comforted knowing that you were her friend to the end.