As for why Edith wanted to tell Edward, not Judith, the Secret...
It may be that Edith had no choice in the matter of who should be told the Secret. I don't know why that might be, but I'm sure that something could be dreamed up.
Alternatively, she may have felt that on the off-chance that the Secret would have to be dealt with physically, Edward would be more up to the task than Judith.
Or else she really wanted to stick it to Edward. "So, sonny boy, you think the Collins family is the best thing since sliced bread? Well, let me tell you what it's really like!" But then Edward arrived too late for her to have her fun, poor thing.