We do not know, if the recycling bin is full of newspapers. If not, then she can put all of the newspapers over over another and measure the height.
Let's assume the height is 50 cm and every newspaper is folded in fourths. If she has 50 newspapers in a bin it means, that a newspaper folded in fourths has:
[tex] \frac{50 [cm]}{50} = 1 [cm] [/tex]
If its folded in fourths it means, that 1 newspaper is [tex]\frac{1 [cm]}{4} = 0.25 [cm] [/tex] thick.
Then, she can calculate number of pages in a newspaper and divide 0.25 by the number of pages.