What is the best evidence to prove that Irene was heterozygous for hemophilia?

The best evidence to prove that Irene was heterozygous for hemophilia would be a genetic test showing the presence of one normal allele and one mutated allele of the gene responsible for hemophilia (F8 for hemophilia A or F9 for hemophilia B). Additionally, if Irene has a family history in which she has a son with hemophilia (who inherits the mutated allele) but does not express the condition herself, it would further support that she is a carrier (heterozygous) rather than homozygous.