@JP  
I mean, she might accelerate the Sun’s evolution until it reaches the white dwarf stage, then move it to accrete material from another star or merge with another white dwarf, triggering a type 1a supernova. It’d never happen in the real world and also be completely overkill (the red giant stage would be enough to wipe out life on Earth), but for a powerful-enough magical pony who wants to send a message, it’s not completely off the table.

@JP  
The Sun has been outputting energy at the rate of about 73 tsar bombas for the last 4.5 billion years and has enough juice to do so for another 5 billion. It doesn’t need to go supernova.
 
 
Also supernova’s yield is pretty much “if one happened in place of the Sun, Earth would get erased after 8 minutes needed for the light to reach it pass”.

IIRC our Sun is not massive enough to go supernova (based on our current understanding of astrophysics), so I’d say the Tsar Bomba is more dangerous.
 
(Though, Tia can move the Sun, so all it takes is a slight nudge in the wrong way and Earth’s orbit goes wonky and we’ll get pushed out of it and then we’ll freeze to death in the depths of the deep space. Unless she keeps moving the star with Earth, in which case the solar system gets destroyed anyway but at least we’ll stay warm. So, maybe Tia.)