She had another bottle of Heineken to pluck up the courage to go to the loo, by which time she was bursting.
I am not sure what the relative clause in the above sentence exactly means and which word modifies. Does it say that she was bursting during the time spent in the toilet or that she was bursting during her way to the loo.
P. S. Does the word "burst" in the conext mean the explosion of laugh (the phrase "burst out laughing")?