'sup bitches, so, okay
puella magi can sense magical individuals but it's not an exact sense
they can also track them by a 'magic signature' if it's not been too long (a day or so) since the magical person has been somewhere
HOWEVER it is not direct at all, more pointing to a general area and saying "Yeah! Maybe!"
in the show it's shown sort of like playing hot and cold, wave your soul gem in a direction and it says "there's magic!"
and since the tower is full of lots of magic users like woah sayaka will probably be desensitized (to her chagrin) and only really notice the more powerful dudes without super trying to pick someone out
plus she's low tier puella magi in the first place so no crazy "close your eyes and navigate by the feeling of their magic alone" things
Does your character have magic?
Do you think it would be strong enough for Sayaka to pick up on?
Would anything obscure your character's magic from her?
Would you rather her not sense it entirely?