Five months is a short time. As she is 27, and if she has regular periods, with no other past or present gynaecological problems, she should try at least for a year. She does not seem to be overtly obese, as per the details provided by you.
Roughly around 80% of young healthy couples conceive at the end of a year of trying, and more than 90% conceive by two years.
Therefore I would advise her to continue having regular intercourse at least 3-4 times per week, throughout the entire month. Healthy lifestyle is important. If her periods come early upto 7 ds, but are otherwise regular, with no missed periods, she should not worry about it at present.