-Could there have been an argument that got out of hand, the person struck her in anger and badly injured her, and then they panicked and decided to finish her off and get rid of her so they wouldn't be arrested for assault? And then left the door ajar and took a box of the fentanyl patches to make it seem like that had been the motive for someone to do something to her? I feel like this is one of the most likely scenarios, even though it's still pretty 'out there'... but it would possibly explain some of the strange behaviors after her disappearance.
JMO, it was likely something similar to this. Someone wanted her patches, maybe even wanted to buy some, but she wouldn't sell. They probably tried to win her favor and trust by taking her on errands, etc. (she was seen at City Hall paying a utility bill) They came to her home again to make her give or sell them some patches. An argument ensued, Betty became angry, perhaps was going for help, making noise and someone grabbed her to silence her. She was injured, probably seriously. They felt they had to get rid of her or she would report them to her family or LE. They were in a hurry (drug addicts) and left the door partially opened.
The alternate theory is that the same drug addicts knew she had the patches. They broke into her apartment to steal them, only to be startled by her sleeping in the recliner chair in the living room (her daughter said she did this because of her bad back). Struggle ensues, Betty is injured and removed from the apartment.
There has to be people living in those apartments who heard or saw what happened.