Dog Killed the neighbours cat

I have a friend who lives in a strata apartment building in Sydney. The By-laws there, say you can own a dog or cat.

In the common-property backyard, her cat was there and the neighbours dog saw it got excited and mauled it. The neighbour also is a resident in the same apartment building, not a neighbour over the back fence. 

It died 3-days later at a Vet hospital, from injuries caused by the dog. It cost her $2000 in vet bills trying to save the cat, as she doesn’t have pet insurance. Apart from proposing a special by-law banning dogs in the building which she is contemplating, can she sue the OC for damages and re-coup the vet costs, or does she have to sue the owner of the dog for vet costs? The attack happened on common-property.