DNA testing is definitely needed here ... but I cannot imagine these parents rejecting this little angel either way. This is but one tiny aspect of why IVF is wrong as practiced now. If this child was not made a commodity at conception and now as a means to lawsuit, then there isn't any commoditization of human life.
They can do DNA testing for the rest of this child's life. They won't suddenly turn around and bond with her no matter what the results are.