Use. You bought it June 26. If she eats one a day beginning today, the 8th one would be gone July 3. That's only 4 days past the use by date. Yogurt that stays sealed lasts past the date on the package. As long as it smells normal and doesn't have mold, it's fine.
Because of the live cultures, I'll eat yogurt up to a month after the use by date, so if I had a child I would let her eat it a few days after (I might not let it get to a whole month for a young child).