For an uncommon, she offers quite a lot of utility that can really help out white in the card advantage department
Glancing at your average Magic card, especially one not found in Magics beginner-friendly sets, is intimidating to say the least, as the cards can be filled with enough jargon to make the game seem incomprehensibly difficult
There are actually several versions of Gandalf in the set (including Gandalf the White, whose color identity will not surprise you), and we show him at different points throughout the story by making him different colors
Without these cards, it's likely White Weenie will return to the "play a bunch of one-drops and pray for no sweeper" play style, which is admittedly a play style that can steal a reasonable number of wins, especially for a budget-friendly deck, but is unlikely to keep the deck as a truly competitive, top-tier option in post-rotation Standard