Why did Lydia suddenly want to commit suicide?

I've just watched this film again and yeah it doesn't make much sense to me. She seemingly goes from hitting out at the deceased couple for the attack by Beetlejuice on her family, who are then seen to be ok afterwards, to writing a suicide note so she can be with the deceased couple in the afterlife? What?

It could have at least done with fleshing out Lydia's interaction with the couple cause it shows them only have two very brief scenes together. Doesn't seem enough time spent to warrant her wanting to commit suicide for to join them. And it didn't make her unhappy enough with her life and family to be of that disposition to want to do it either. If it was that attack that triggered it and she thought the deceased couple were to blame, then it makes even less sense.

Because she is Goth