i lost my father alaha veshalom 4 months ago just call her and tell her how sorry you are for their loss and ask if theres anything you can do from where you are to help her if she has the time just talk to her like a normal person have a normal conversation from my experience when i was sitting shiva it was horrible when people came and were just depressed the whole time because the whole point of being menachem avel is to comfort them so just act normal (or as normal as possible) also try calling at a time when not so many people are around meaning not the middle of the day (that was always the busiest for us)
you can also send a letter bt that does not get to the person until about a week later so it all depends how close you are with your friend