The glass box, and what attacked the couple?
I'm new, not sure if it's OK to refer to a later episode--?---
At this excellent Twin Peaks Wiki, it's explained that "The Experiment" - as this character is listed in the credits, is seen again in episode 8. I'll leave the link for you to read the rest of the info, so I won't be posting a spoiler about episode 8 if you haven't seen it.
Can't be Laura Palmer, she was born as a symbol of the good side ( remember, the golden orb that the giant and the fat lady revealed and send to the world, as a response to Bob's orb from the atomic bomb ??)
Yes, indeed - You're correct, it can't be Laura Palmer. People who theorized about her being Laura earlier on this thread were writing before episode 8 aired. As per my previous reply, the woman/thing from the box is The Experiment, as credited in ep 8.