R, easy to prep 1-2 spheres in fog of war too. Congrats that alone may 100-0 enemy ADC even if you're not fed if you itemize properly.
One full rotation of basic abilities at level 18 is:
Q: 230+65% AP
W: 230+70% AP magic and 46+14% AP true
E: 250+60% AP
Total: 710+195% AP magic and 46+14% AP true=756+209% AP
With no spheres out, her ult is another:
540+60% AP, with each sphere out adding, 180+20% AP. Getting 2 sphere's is easy, even 3 isn't too hard (you can get 4 if you play it well, theoretically 5 with 45% CDR and the 8 second duration but idk if that actually carries through to ult, never managed to do more than 7 sphere ult in a real game myself and that has been only rarely.
0 Spheres out: 540+60% AP
1 Sphere out: 720+80% AP
2 Spheres out: 900+100% AP
3 Spheres out: 1080+120% AP
4 Spheres out: 1260+140% AP
Those numbers are just ult itself, if you add in basic abilities, including landing more than one sphere in the 2+ sphere's out case and you can see how ridiculous her damage output is, raw both burst, and extended combos.