Talk to Gynecologist on Friend's Periods Were Late, She Took Primolut N For 5 Days (3 Tablets Each) But Got Light Periods

Hey, my friend is 23 years old and has been having irregular periods throughout 2022. she was 82 kg and is reducing her weight through diet, cardio and weight training. her due date of periods was sept 1 but she missed it. she took primolut N on sept 9 to sept 13, 3 tablets each day. today she got her periods but it's little to even use a pad. the periods blood is either like a watery texture, or it's a thick blood. but overall it's not too much, it's dark red, light brown etc.

it's first day, the lower abdominal pain is there but she's not having heavy periods like she had last month. Can anyone uggest what's the problem?