How to treat a woman whose cycle varies from time to time. how can she make it stable so she can calculate her ovulation dates?

Challenging: If she is regularly irregular---subtract 14days from the period interval and that is generally when she is ovulating. Example periods every 1. 60 days minus 14 = ovulation every 46 day 2. 90 days minus 14= ovulation every 76 days if irregulalrly irregular- next to near impossible- have intercourse every other day as sperm will live in cervix up to 72 to 96 hrs. You should have hormone tests!