In addition to working a voice talent I'm a certified vocal instructor in a technique that was designed with vocal surgeons and is medically proven to prevent and reverse vocal damage (used by Michael Jackson and tons of grammy winners, etc).
From what you're explaining I bet I know exactly what's going on and how to fix it.
When we use the voice incorrectly it sets off a chain reaction. The end of the chain is determined by what exactly you're manipulating. It can happen with singing or in VO (especially character VO). The result is pain, strain and many times loss of voice, nodes/polyps or worse when it goes on for a long time. The fact that she's already had nodes says she's connecting her vocal cords in a way that is unbalanced. But it can be fixed.
In your friends case, I'd put money on the fact that she's belting incorrectly or 'pulling chest' when she sings. Lots of people do it to get more power and push through the high notes. I was a professional studio and live singer and was a horrible belter for many years. I still did VO and session stuff but it caused loss of my voice and loss of some of the areas in my voice I needed for VO if I had a session the next day after a long gig.
What she needs is to learn to identify what she's doing that's causing the chain reaction and learn how to get a better result: expanded range, more power in a way that feels easy (even on power stuff) and develops a healthy, strong voice.
I teach online via Skype and have students in several countries. There's also tons of free information on my site: blog, videos and other good stuff: www.thevoiceclub.com