I've spent about 15ish half potions already and I'm close to my 3rd copy for 2/4 stars but I can say for sure that unless I get lucky and find her twice from drops within the next couple days of what's left of the event, I definitely won't be to fully break limit her. I hate it but I may have no choice but to wait for the reprint event.
Honestly, with how difficult it is to get items without whaling away at potions, I don't see any reason to get grimoires for anything under SSR, and even then it's a decision between the event unit/weapon/other rewards or that.
There are other kind of events in this game but I'm not sure how much better or worse they are in comparison but the biggest overall problem is the simple fact that grimoires seem to be only available from events.