• One article I read said the boy managed to fire the round that was in the chamber. When carrying a concealed weapon, is it common to keep a round chambered?

Yes. Not only common but recommended. Without a round chambered you've got a club.

• Does the firearm in question have a safety? If so, does operating the safety require a degree of force, knowledge or dexterity that it would prevent a toddler from disabling it?

Skimmed the article didn't see the mfg/model listed.

• Is a zipper considered sufficient protection to avoid the weapon being accessed by someone other than the owner? I've noticed that police officers secure their guns in the holster with a simple snap, so it seems like a zipper may be even more secure. However, the holster is worn on the body, so it's easier to feel if someone is messing with it. Also, it might take more force in the fingers than a toddler can muster to undo a snap than a zipper. I just don't know. Would experienced gun owners consider a zippered compartment in a purse to be sufficient to keep the weapon secured?

Personally no, not a fan of 'off body' carry for lots of reasons, this included.

• News reports say the woman was accustomed to carrying the weapon on her hip, but that she got this special purse with the concealed carry compartment for Christmas. Are there different established procedures for securing a weapon that's physically on one's person as opposed to stored in a purse, backpack or other bag?

Yes.

• Do people who regularly carry ever use trigger locks, or does that defeat the purpose of having the weapon at the ready?

No. See chambered round above.

• There seems to be a concerted effort in the stories I've read to paint the woman as a responsible gun owner and the incident as just a tragic accident. Do other gun owners see it that way, or could the woman have taken more precautions?

I'd fall into the tragic accident category