The emergency vet was right. According to the 2005 edition of Veterinary Technician magazine (article found here: http://www.aspca.org/site/DocServer/Wallis-Tox_Brief-May_VT_05.pdf?docID=4702 ). Ingestion of avocado is known to cause gastric upset (most commonly vomiting and diarrhea) and should be treated symptomatically.
What this really means is that as long as your dog is feeling and acting okay, you only need to monitor her and make sure she stays feeling fine. I'd actually be a little more worried about her getting obstructed from eating the pit than I would be about her being toxic from eating it.
Just keep your eyes open for excessive diarrhea/vomiting. If your dog goes off feed, becomes lethargic or begins retching without anything productive coming of it, then I'd take her in to see the e-vet.
I hope this makes you feel a little better!
Hi again Bearpie~
I don't think you have to worry about 'possible' heart problems with your dog. From the articles I've read and the research I've done, your pup would have either had to have eaten a lot more avocado or would have had to chronically eaten it.