The fact that the Catholic hospital personnel "could" lie about administering the ovulation test would seem to be an argument against many, many medical procedures that "could" be used fraudulently.
For instance, one could argue they shouldn't do hysterectomies for legitimate reasons, because hysterectomy "could" be used simply to prevent childbearing.
Or, that they shouldn't treat ectopic pregnancy, because it "could" be a cover-up for a direct sterilization.
Or, that they shouldn't make liquid morphine available to treat pain in the elderly, because it "could" lead to euthanasia of the "terminal sedation" "Liverpool Care Pathway" type.
But that would be wrong, wouldn't it?
Every rule is only as good as its oversight and enforcement.
The raped woman has a right to defend herself from insemination by the rapist, which is an extension of his assault. She can do so licitly if it's done before ovulation (therefore cannot be abortion). Is it right to deny her this legitimate self-defense because some "could" abuse it?
Serious question. I am unalterably opposed to abortion at any stage, including pre-implantation, for any reason. But a non-abortive defense against rape-insemination is a different matter, don't you think?