Why did Serena cut her hair?

Many of you want to know why, the answer is simple. The reason why Ash wasn't surprised compared to Clemont and Bonnie were because it was a nonverbal message that was understood in Ash's Japanese culture. In traditionalist East Asian cultures, one cannot shave or cut their hair because they would offend their family members and ancestors. They could only do it in the most dire of circumstances. Cutting or shaving the hair represents determination after a loss, guilt or humiliation. It also symbolizes a new start. By cutting her hair, Serena was telling Ash that she is determined but also at the same time she idolizes him as someone amazing like how Ash says Dawn is the best.

Ash seems to harbor feelings for Dawn, Dawn acts tsundere towards Ash.

Serena harbors obsessive feelings for Ash but Ash appreciates her help in some form.

So to complete the trinity, how would Dawn and Serena see each other, aside from shipper headcanons?

Some Japanese fans believe that Ash in XY is acting a lot like Dawn, with some high fives and adopting Dawn's catchphrase Daijoubu.

At this point, I have reconciled Pearlshipping and Amourshipping. They're not opposed to each other at all but are rather complementary to Ash's development. Both of them are different in many ways while they share similarities and overlaps. It's interesting to see Serena develop as a character who is almost the reverse Dawn. I do feel that Dawn and Serena if they were to meet, would become very close to each other. With Dawn seeing Amourshipping, while Serena does the same for Pearlshipping. If it does happen, the writers especially Atsuhiro Tomioka have created a shipping truce between Amour and Pearl. Unprecedented in the world of Pokemin shippings, but I could see it happening based on my Sun and Moon theory. Admittedly, Serena is starting to grow on me. I think she could only get better to the point that she literally rivals Dawn in terms of personality.

So when comparing Amourshipping and Pearlshipping, the two are very much opposites. In Amourshipping, Serena is the yandere Ash and XY Ash is a non-tsundere Dawn. In Pearlshipping, Dawn is the tsundere XY Ash and Ash is Serena except without the yandere obsession.