I agree. Question really is who put a real bullet in that gun? Baldwin didn’t. Was the intention to kill her or to frame him?
Not really.
The Armorer or designated Weapons Handler should have personally checked the weapon immediately before it was handed to the Actor. That is the industry-standard practice.
And the Actor has the right (but no obligation) to check the weapon again. Standard practice in the film industry. Offends the purists who live by the "four rules". But actors are assumed to be trainable chimpanzees who cannot be trusted with firearms. The industry practices are made to deal with that problem. If they are followed and enforced, they do.
Of course, there should have never been live ammunition anywhere on that set, as the script did not require a live fire session. Nor should other cast members have been allowed to take any weapon after hours for recreational target practice.
Besides, it was a setup for a rehearsal. They should not have had any firearms issued to the Actor at that time.
The mistakes and negligence keep accumulating. At some point, luck always runs out.
Was the intention to kill her or to frame him?
This is way too clever a plot, suitable for movies or novels only. In real life, arrogant people commonly do stupid, negligent things and sometimes it catches up with them.