Girlfriend's mother has cancer how can I help?

My girlfriend's mother has been diagnosed with cancer about a week ago I am at a loss sometimes as to what to say to her(my girlfriend).  Here's the hard part we are in a long distance relationship, she lives in another country I am planning a trip to go and see her in feburary, but she's going through a hard time now and I'm not sure what I can do or say, if we lived close there are lots of things that I could and would do, but I am not with her.  I talk to her everyday, mostly at night, but sometimes during the day if she has time, I have told her on many occasions that "I am here for her if she needs anything" and "anytime she wants to talk to someone, day or night I'll be there".  Sometimes when we talk I'll try to cheer her up a little, sometimes I tell her jokes, but usually only on her request because I know that when your feeling bad you don't always wanna here jokes.  I'll even sing her songs(she's Latino so she really likes this)and if it helps I'm more then happy to do it, I could care less that I sound horrible as long as it helps her feel better.  But it's nights like the other night when she was crying her eyes out, I felt so bad for her and so badly wanted to be able to hug her and console her, and I have never felt more helpless in my life.  I didn't know what to say beyond telling her that she'll get through it and that i understand how she feels.  So if anyone has been in a similar situation, I would be interested in knowing how you handled it.  thanks in advance