But I don't understand the pervasive resistance of arrest that normally precedes these incidents. 

I't is my understanding that the police came barrelling in the door behind a battering ram and with no verbal warnings.  Not much time for resistance.  Almost like they were looking to get shot at so they could shoot back...

I'm not an NRA type of guy, but I don't think she was unwarranted in attempting to protect herself and her property, given that she was a) in a violent neighborhood and b) otherwise defenseless.

IF the police gave proper warning and were visibly identifiable as officers of the peace, they might have a leg to stand on.  Given that they couldn't ID the perp as an old lady, I'm guessing she couldn't ID them as cops.  I'm also guessing they were wearing body armor, and it's a sure thing that she wasn't.