Going out on a limb here, but IMO forget her legality or not. She's not who you should be worrying about, even though she was prepared to assist him.
You need to talk to the police. I've twice met men (one = ExH) who went to the lengths of setting up situations using others to knowingly lie, entrap, and help them manipulate their target.
Try and step back and think about this in terms of what is 'normal' in shitty behavior vs what is really unusual.
People who do this don't worry about the risks of getting caught, or the people they are using turning against them and turning them in. Why not?
Because: they believe they will be able to control them too, and that the people they use are disposable. (in ExH's case, literally)
It's not 'normal shitty behavior', it's another level and a warning sign.
The two I've come across were very different types, but what they had in common was superficially charming, positions that gave power, and people around them missing, and many women had allegedly used and betrayed them. Both operated publicly and dangerously in terms of potential of being caught.
Both went from more 'minor' (ie nasty but not clearly illegal) set ups, to very serious behaviors including kidnap, and arson in order to maintain control and/or cover other lower crimes. You wouldn't have guessed looking at them.
It takes a level of ego, entitlement, and an underlying belief that they are smarter than others around them to manipulate using others on a organized level.
They are quite simply dangerous, especially when they are bolstered by getting away with it, either through malice, or the lengths they will go to to cover up.
My experience is they will play the long game returning again and again, sometimes with many years in between because they are rotating what they are doing to who, and finding others (often vulnerable and lonely who look up to them) to bring into their schemes. They can return when children are older.
The worst is when they finally get spotted doing something serious enough, it turns out that there are serial victims.
They were manipulated, left confused, embarrassed, not taken seriously, and blaming themselves for not seeing it earlier, and stayed quiet. Sometimes they had been dragged into doing things to others themselves and afraid of what they did. I'm mortified that I could have been targeted twice, but the reality is they know who'll make good prey, less likely to go to the police, or be believed.
It may be that your H had just started down this road, and has scarpered when busted. But I'd put a high likelihood that he will do this again, be it with you or another, and next time it will be done better, because he will have learnt.
I don't mean to scare you and would like to be wrong, but prepared to be called whatever by everyone, to raise it.
Please, secure your rights with your child and take this to the police, because while you may get nothing out of doing it now, it may protect you and others later. This kind of behavior is way beyond normal and nearly always ramps up.