Alam ko ang stress ng delayed period, especially pag uncertain pa! Kasi naman may PT na siya two times na and both negative, pero kung gusto niyo talaga ng peace of mind, yung blood test (beta hCG) ay mas sensitive at accurate talaga, lalo na kung mag-check na siya ngayon, parang sure na yan kung merong bun in the oven or not, so I'd say go for it na lang para kayo ay makasiguro na. But honestly, best thing is para sila makonsulta with her OB kasi marami ring reasons bakit delayed ang period (stress, hormonal changes, weight fluctuations) and doc can check if may ibang nangyari, so definitely suggest that din!