If the 8% is per year, we need to calculate the acquired value after 20 years with compound interest.
Formula :
AV : aquired value after 20 years
V : starting value
r : rate
y : years
AV = V x (1+r)^y
AV = 10 000 x (1+0.08)^20
AV = 10 000 x 4.660957
AV = 46 609.57
She will have available 46 609.57 $ after 20 years with compound interest if she save 10 000$.