But if her gimmick were "build AP to increase physical damage spells", why would you ever use her? AD champions are already strong and abundant, and she would have a really hard time buying the stats she needs (AP + armor pen), meaning that basically any other AD caster would do better. Most other stats would be wasted: crit, attack speed, lifesteal.
Azir is probably the closest counterpart, a weird marksman whose attacks scale with AP instead of AD, but that works because AP/AS are still available on items without any wasted stats (he can use CDR, mana, MP5, and health too).