Unfortunately, there is little evidence for the efficacy of the Shettles method, so if you attempt it you should be prepared for the possibility of having another boy. If you nevertheless choose to pursue it, here are some possibilities to raise with your rav (along with the questions about its efficacy):
It is possible to delay ovulation medically under the guidance of a physician, as with estrogen at the beginning of the cycle. In some cases, medical treatments or complementary medicine techniques may shorten bleeding.
There are also various halachic measures that can sometimes enable a woman to immerse earlier than she has been.
Our article on Ovulating Before Immersion, and our posted questions on the topic, detail these medical and halachic approaches, laying out the possibilities that would be relevant to discuss with your rav. Since your case is not halachically equivalent to that of an infertile couple, you cannot assume that a given leniency applies to you without first raising it with your rav.
Behatzlacha! Please contact us with any further questions.
This response was updated on 13 April, 2021.