Yeah, it sucks to spend time on a project and have it yanked. Totally. But did Marvel do anything actually wrong? No.
We don't know the full details of why it was pulled and we probably never will. But Marvel clearly had their reasons. They're not in the business of throwing time, money and effort away so something about this book wasn't gelling the way they wanted it to.
Doesn't mean that Cain and her collaborators weren't doing good work, necessarily, but that it perhaps didn't jibe with Marvel's expectations.
We don't know why Marvel cancelled it. Assuming it's simply a continuity issue seems flawed. That's something that could have been overcome fairly easily.
Think about it - Marvel paid the creatives involved in full for work that Marvel will never be able to recoup their investment on. No way they did it "just because" or due to it not lining up with other plans. I think they were just unsatisfied with it and decided to pull the plug.
Cain is within her rights to bitch about it but I think the wiser route would be to express disappointment and move on. Marvel isn't coming out and saying "we dropped it because it just wasn't cutting it" or that "hey, it sucked so bad it was better for us to cut our losses."
It's a difficult situation but it's always better to keep it as professional as possible.