Thank you! This is a great question and one that I can somewhat answer.
Canine search dogs All are very different and have very different purposes.
http://www.ussartf.org/dogs_search_rescue.htm
The article above explains that there is a difference between an Airscent dog, tracking Dog, Trailing Dog, Cadaver Dog, etc. if Elisa was already deceased in water on the roof and they only had the canines that tracked her LIViNG scent or Airscent dogs, they would not be very likely to hone in on Elisa's deceased body. However, if a cadaver dog would have been brought to the roof, it most likely would have picked up on her scent. This may just be a case of detectives not believing a victim was deceased and choosing the corresponding SAR dog to track her living scent.
Man, you would think a canine SAR unit would have all the tracking, trailing, and cadaver dogs working. Maybe they were too busy sending the extra dogs over to find Chris Dorner? The idea alone makes me so sad.