That's just a theory, but either way this is fanfiction. People change stuff all the time for their own works.
Maybe so, but let's be honest here, Sakuya is a human and will probably waste away while the rest of the scarlet resident stays the same unchanging, so unless Remi turns Sakuya into a vampire, this'll be the course of their destiny.
Actually this wouldn't happen, seeing as how Sakuya uses her time powers to stay young.
If anything, it ought to work the other way around. A person who could stop time for everyone but herself would presumably keep aging while the rest of the world was paused, i.e., stop time for 30 subjective seconds, and when it resumes, you're now 30 seconds older than the rest of the world. Do that often enough and the gap becomes perceptible. To your own perceptions, you've lived as long as you would have anyway, but from everyone else's perspective, your lifespan was shorter.
Maybe so, but let's be honest here, Sakuya is a human and will probably waste away while the rest of the scarlet resident stays the same unchanging, so unless Remi turns Sakuya into a vampire, this'll be the course of their destiny.