@Crowley
 
Certainly.
 
You can look at it another way. Zecora took the gem, because she already knew of Spike’s greed. She probably recognized that a lot of his problems were going to be related to him wanting to keep the gems he had acquired.
 
So karma may not have been necessary. Her taking the gem might have just been a way for Spike to lose some of what he already had. You can’t be greedy about something you don’t have.
 
I think that if this was what Corey Powell (I think that’s the writer for this episode) was going for, then Zecora gave the gem to that Girl Scout pony so that the audience didn’t think she just took the gem and kept it for herself.
 
But your explanation works just as well, if not better.

I just realised… (spoiler alert)
 
Zecora mentions negative karma was the cause of his problems with the animals. Then she donates one of his gems to charity. By the end of the episode, the “positive” karma from that kicks in (just as Angel’s about to kick that train seat) and his luck turns around because of it.
 
Zecora sneakily saved the day.

I most confess my dragon friend Spike,  
Your booty is one that Zecora quite likes.

knew it was gonna happen.