The skin’s natural turnover is more than 18 days. As such Tretinoin, topical antibiotics, or similar are unlikely to lead to improvement in 18 days. Treatments that focus on cleaning or unclogging pores are more likely to have a positive impact within this period such as over the counter products (benzoyl peroxide, salicylic acid), or just partially concealing with makeup before event.
I know this isn’t what your daughter wants to hear, but most kids are more sensitive to the appearance of their own acne than others. It’s not the end of the world. If it were my child, I wouldn’t support corticosteroid injections for what sounds like not severe acne. I’d instead focus more on why it is leading to “desperation and low self-esteem” and ways to improve that.