Late PMS cycle. Some thoughts on this,

A friend of mine is having hard time with her PMS cycle. Her last one was in Feb 22nd (the first day in her previous cycle), but until now (March 29th) she has not had the next one. She had tested herself with several testpacks and all the result was negative. She showed no symptoms of being pregnant (no morning sickness, not easily get tired). Just in her usual self. She has not taken USG yet--I may need to suggest that to her. If this is helping, I remembered her doing the diet stuff with some blended fruits and veggies smoothies (banana, bok choy, spinach, dragonfruit, skimmed milk or low fat milk), referenced from some YouTube channel, with no accompany from nutritionist. I suspect that this has something to do with her problem. Please kindly give me some thoughts on this, thank you.