Bitter is off on her own now and worrying about self-defense. Good for her - I wish I could have managed to get that message across to some young women I've known.
One of them, a relative, could never be troubled even to lock doors. She had been brought up out in the sticks, after all, and forgot about how they had dogs and other deterrents. I deliberately showed up in her apartment unannounced a couple of times when she knew I didn't have a key, but she never got the message. She's older now, married with kids, and now she leans more toward the paranoid end of the spectrum.
Once I lived in the same apartment building with a friend and coworker who likewise acted invulnerable. What made it weirder was that she had a stalker at the time - although he lived 400 miles away, it wasn't hard to imagine him driving up.
She would at least lock the door, but she wouldn't use the deadbolt. Then one day I borrowed a dinner knife from her, had her lock her door, and I was in her apartment about 5 seconds later.
Did I make an impression? Oh, sure, but don't go thinking that she started using the deadbolt. Some time later she had effectively moved in with her fiance and the apartment became a warehouse/bargaining chip. And when she needed something from the apartment, she'd call me and ask me to break into her apartment and bring it to her at work. That was known to include lingerie - I just knew that one day I'd get caught and nobody would ever believe my story.
Basic security isn't that hard. Your external doors should have deadbolts, perhaps even the kind that are keyed on both sides. If not, it's no trick to put them in, and a landlord shouldn't pitch a fuss. Of course it's no help if you don't use it.
Door chains are good, but I like these* better - IMO they're a lot sturdier, they're quicker to use and more resistant to defeat once the door is open. But you can have both if you want. Throw in a surface-mounted bolt too if you like - $20 would get you all three in most places.
Then there are door viewers. These can be had for less than $5 and permit you to see out with the door closed. Most motel rooms and many apartments will already have them. Sure, someone can cover the viewer, but then you know someone is there, don't you?
Sliding glass door security can be had fairly cheaply too - just lay a length of dowel stock in the tracks. Screens are no defense at all.
There's much more that can be done quickly and cheaply. Do it now!
*UPDATE - I was sure I'd find a link for what I was looking for, but then I spaced out and didn't find one before posting. Whoops, now I'll find it or I'll change my name to Ishmael. What? - no luck at Walmart, Kmart, Lowes, Home Depot, Ace Hardware, and True Value Hardware (and I won't link any of the @#$! because they failed me). Alright, I do still have a life, dammit. Anyway, the one moving part is shaped like a tall skinny U connected to a mounting plate by pins at the open end that permit the U to swing in a horizontal plane toward and away from the door. The U engages a protrusion mounted on the door, which can slide within the U to permit opening the door a couple of inches. Other details are such that you can easily flip the U to engage the protrusion when the door is closed, but not when it is open. You've probably seen them in motels and elsewhere - you don't fumble with a chain, it requires no manual dexterity, and unlike a bolt you can still open the door a crack.
Oh yeah, if you mount something like this use nice long screws so you connect to the structure of the house. If the screws only hit trim and drywall they will have no strength.