The App (Drip) gives you after about 3 months acurate times on when the period should start. If you want accurate fertility tracking your girlfriend will have to measure her basal temperature (ar best daily) and either look out for changing cervical mucus or change in cervix opening/hardness.
My friend your first steps that you should do right now are: Get up from the toiltet Grab a glass and drink it Then make yourself a sandwich Then continue from there