Charming story. I giggled at the fertility doll prank, and loved the antagonism/grudging affection between the siblings. The part with El Viejo had me scratching my head because it felt like it came from out of nowhere. Old guy witch is threatened by competition? And wait, the sister has powers as well? That actually took some of the charm from the story--although I did laugh when she decided to leave last Thursday and actually did it. I don't think the whole "You can do magic too" needed to be explained--just have her stomp out and let the audience figure out how she did it. She's obnoxious enough that it can work, magic or no magic.
I also liked the multi-ethnicity shown in the story, though there were times I got a little lost discerning the adult characters. Was trying to figure out if both kids were mixed Korean or if they were a blended family, then realized it didn't really matter.
On a side note, in college, I also, for reasons I had no clue whatsoever about, wrote a love letter to a guy and mailed it out to him. As soon as I put it in the mailbox (for there were mailboxes back then), I did my hardest to cram myself into the mailbox to get it back. No such luck. And sadly, I wasn't a witch, so the letter was mailed out to him. What followed was a very, very awkward phone call, in which I have thankfully blanked from my mind, but had him pretty much saying he wasn't interested. The irony is, twenty years later, we're now co-workers and pretty good friends, though if I need to send him correspondence, I get my hubby to do it.