I can tell you now that she has no idea that the stains on the jacket is blood. I haven't seen that phrase (pink elephant) used that way before but I think I get what you mean (and no, no alcohol involved).
That essential little detail regarding dad's absence is actually something that's giving me a very difficult time right now as I write the next few chapters. The thing is I can't find a way to effectively explain it without having to switch the PoV from Derek to another of the characters - that is at least without it resorting to a boring narration. We'll see I guess. If I can't fit it all in maybe it's something to discuss another time... say in a sequel.
But yes, Derek's mom is quite aware of who her husband is. She did after all make a lot of sacrifices to make things work. As such, she is or was afraid that Derek would take the same path.
Neither Derek or his mom will have the chance to warn Mrs. C about anything. The story is about to enter a spiral and they have other things to worry about. Not that Mrs. C won't find out on her own of course.
And yes, there will be a price to pay... there always is.