She has a low amount of magic for an elf is the key phrase there. It would still be sizable compared to most other races, but compared to her peers and her people, she's a complete failure in that regard.Iris said that an elf can't use the breast potion do trough their high amount of magic, but Tirria said that she has low amount of magic for an elf. Is that a future plot point or am i just interpreting it wrong ?
Pretty much this. I wanted to add breast size changing potions, but also didn't want to trivialize her storyline by just chucking a potion at her ^^;Both can be simultaneously true with her amount of magic being somewhere in the middle especially since plot wise it would kinda screw up her character if a potion could've solved the size insecurity issue even if just on surface level
So she's in that awkward area that there's too much magic in her (modest) chest for potions to affect it, but not enough magic to cast spells well like other elves. It also doesn't help that elven spells are notoriously inefficient, but as a matter of pride (and stubbornness) elves refuse to modernize or re-evaluate their spell library.