Q. In the above case, (A prior already married couple [to each other] that is now converting and going to the chupa on the same day as the tevila), If she made a hefsek does she have to keep full seven tahara days, or since by converting she is like a newborn?
 
A. Horav Shlomo Miller’s Shlit’a opinion is that since niddah impurity laws do not apply to Gentiles, as long as she made a hefsek before immersing for the gerus tevilah, she would be permitted to her husband with that single gerus tevilah. (See also Igrois Moshe E. H. 2: 4)
 
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a