I know it's hard considering either Lily incest-poisoned your brain so much or that you are being pressured into seeing incest so that you don't anger your beloved, there's something you need to know:
CATRA. AND. ADORA. ARE. NOT. AND. NEVER. HAVE. BEEN. "SISTERS!"
Firstly, that page from the "show bible" calling them "sisters" was made by NBC/DreamWorks/Netflix without ND Stevenson or any of the other creatives, way before the show entered production; before Stevenson and the crew ultimately made Catra and Adora childhood friends, NOT "sisters."
Secondly, like many authors commissioned to write tie-in books to popular kids media, Tracey West was completely unfamiliar with She-Ra, meaning she KNEW NOTHING about the plot or the characters.
So DreamWorks (in collaboration with Schoolastic), without any input from Stevenson or the show staff, gave her information sheets that would give a simplified run-down of the show's premise and characters.
And, of course, they would contain the faulty, outdated information referring to Catra and Adora as "sisters."
Also meaning that these tie-in books were planned before the show was even made, before any of the creative decisions made by Stevenson and the staff.
How do I know this? Because this a very common practice for companies. Getting third-party writers to write tie-in material for their media without any of the original creatives involved.
If Lily or Mikalia knew anything about show-production and franchising, they would know this sort of thing happens all the time.
Mikalia, it seems like you and Lily so desperately want them to be sisters because (as I've said before) if they were, you two would constantly ship them like you do with Jinx and Vi, Tai and Kari, Zuko and Azula and Gorion's Ward and Imoen.
If you're not being being pressured into Lily's incest-fantasies then just admit you have an incest-fetish, admit you are turned on by sibling x sibling love; admit you are proud pro-shipper.
We won't judge.
Buuuuuut if you did all of that, that would also mean knowing all about Lily's sexual abuse of Courtney, her sister.