I haven't seen this idea suggested, so thought I'd throw it out there. I wonder if a neighbor (or someone she thought lived there) asked her to help move something into an apartment or from one to a dumpster. Since she'd most likely need both hands to help carry it, it would make sense to ask her friends to watch the dog for a minute while she did it. She would have expected to be right back, and may have just dropped it off and hurried back to assist. She could have helped carry something inside and been attacked and murdered there, and then carried out to the dumpster. On the other hand, she could have gone inside with the person to help carry out something heavy, been attacked and murdered, and then the item was taken out with her inside.
The friends most likely thought she'd be back soon, since she was (speculation on my part) usually true to her word, and just tied the dog up thinking it would be just a few more minutes. All MOO