junior I do recognise it now as I have been diagnosed for 12 years. However, at the beginning altho i knew something was wrong i couldn't work out what it was. It grips you. It also self perpetuates so the more it goes on the worse it gets. It also is easy and dare i say it enjoyable to allow yourself to be sucked in.
The delusions, altho creating conflict, are comforting in a way. As you don't have to question yourself and metaphorically drag yourself out of it. You have to really reach into the tiny part of yourself which is questioning your behaviour. It is very hard.
You also have to make small goals like go to the shop on your own etc. Sounds mad (and it is!) but it would take days to build up to something like that.
The other thing I did, (which you haven't mentioned) which was really bad was 'self medicate' with alcohol. If anything like that is happening it escalates much quicker.
The issue here is whether talking to her H will increase her sense of paranoia? Also, she is still an adult and needs to be treated as such, so i would approach her first.
Try asking how she is, you could use the broken rib incident to guage whether she realises that is unusual. Ask if she wanted to leave before her DH got come but felt incapable? If she says no it isn't odd she had to wait for DH then you could explain how dangerous it could have been.
There is no real right and wrong, and she will be upset whatever happens. I would look at bipolar/mental health websites about how to deal with those (not that i'm saying she is bipolar, but the appraoch may be useful) who are acting irrationally.
Good luck. I really feel for you. :)