Hi Lora
It means:
She was about to go nuts, because of the fact that they were so many.
She almost got crazy because they were so many.
She almost flew into a tantrum because they were so many.
At være ved at X: to be about to X, to almost X. Alternatively: to be doing X.
Jeg er ved at blive skør: I am getting crazy.
Jeg er ved at male: I am painting.
Jeg er ved at begynde: I am getting started.
Kuller: tantrum, истерика. At få kuller: to get a tantrum, to go nuts.
"af, at": because of, because of the fact that.
Jeg er træt af at male: I am tired of painting.
Hun blev skør af, at de var så mange. (notice the comma, because the second part is a sentence and not just a verb or noun).
At være så mange: to be so many [people].
Martin