Is it normal for people going through cancer to totally chance their personality & become depressed?

My best friend was diagnosed with Hodgkin's Lymphoma over the summer & has totally become a different person. She was the Prom Queen last spring and now she's like totally withdrawn and doesn't Facebook, doesn't return calls, is always fighting with her parents, broke up with her boyfriend who is like the guy every girl wants and is now dating a 29 year old, and she doesn't like hanging out with her friends anymore and spends all her time with him instead. She said she never sleeps anymore and stays up doing art instead, and her art has become really dark. She started chemo in late August, Idk what else you might need to know. So is this normal? Like I said, just last spring she was super popular, straight A's, totally pulled together perfectionist dancer girl and now she's a train wreck. She said she's going to never be able to have kids. Is that really true? I mean, it's just a chance, how could they know that for sure already? She's just 17.