There are many inheritance pattern for achondroplasia
not just dominant and it can be known only by genetic testing
of the individual.
I don't think its possible to have a normal stature girl with affected parents if its autosomal dominant. So it must be due to sporadic mutation
in parents, which has not been transferred to the girl.
I can not surely tell the probability, but I can surely tell that if the girl does not have any dominant gene than her child will be absolutely normal, which can be known only be genetic testing.
hope my info helped you
Dr Hari Om Chandrakar