1/4. Since "tasting" is dominant, it can be represented by T. If they have a daughter that is not a taster, her genotype must be tt. Finn and Maggie must be heterozygous, Tt. Therefore, the Punnett square is:
So, there is a 1/4 chance of any child being a non-taster, regardless of how many children they have; the probability is always the same.
40 years teaching Biology and basic Genetics