Request from a new author paraphrased: The beginning of my novel is great, but now I've hit the middle and I know roughly where I'm headed (major plot points) but have no idea how I need to get there! Help!
I personally don't plot, but it sounds as if we have someone that does a modicum of plotting here. My first instinct (which she later said was sound) was that she needed more structure in her process. If you're a pantser, how you get to that next point you're sure of isn't usually an issue. So, she needs a little more plotting in the mix.
She is currently at C and needs to reach the next plot turn at G. That means figuring out logically how the characters would try to reach G and what roadblocks or complications might be in the way. Depending on what happens in that brainstorming session, she might have to tweak the perceived future plot points. IOW, something that happens getting from C to G might slightly change what she thinks should happen at M.