Thinning cervics/early labor

My daughter had cronic yeast infections. Her vaginitis specialist had her on diflucan on 6 months off 3 for about 3 years. Her first pregnancy she has issues with thinning cervics and premature labor. Her son was born 6 weeks early. She is pregnant again in her 2nd trimester and is having difficulty with thinning cervics and premature labor. Could this be happening because of the large dose of diflucan he had her on? Family history, my mother carried her babies full term with no issues, I carried my children full term with no issues, and my daughter has issues.