Cactus in Flower

My daughter has been nurturing this flower for many years. No, scrap that. She started off by nurturing it, and nearly killed it. Now she leaves it to languish on her windowsill, and occasionally throws it the dregs from her water bottle. On this, it thrives! She noticed a couple of weeks ago that it was started to produce buds, so she has been waiting patiently. Today was the day!