Hydaelyn is not evil. I'm of the theory that the crystal itself is a giant auracite crystal. Why? Because the Crystal Tower itself is made entirely of auracite, and has the same glow as her own crystal. This would explain why she hasn't been gaining power and has just been losing it. Just like with any auracite, there's a finite amount of power in it, and she has been expending it over the many Calamities, and it slowly being eaten over them as well via primal summonings. She hasn't spoken to us because of the constant primal summonings for the attempts at the 8th Calamity, she's been trying to conserve power as much as possible. Just think about it, Sephirot (Elder), Sophia (Elder), Zurvan (Elder), Bahamut (Elder), Phoenix (Elder), Alexander (Elder), Ifrit, Garuda, Titan, Ramuh, King Mog, Leviathan, Odin, Ravana, Bismarck, Knights of the Round, Susanoo, Lakshmi, Shinryu, Eureka (Elder), and finally Tsukuyomi. This run to the 8th Calamity alone has had so many primal summonings that she's being completely drained of her own power, and that's being added onto the Flood of Light and Eden. She's working on fumes at this point.
Which means us meeting with her probably in Patch 5.55 is the sign that this is indeed the end of the line, she probably is out of options at this point and can only push us forward one last time to where we need to go.