Wow, that's a tough one.
I can see both sides I think. Think of it from her point of view-if there is lots of money to be made, and she's seen him be successful before, and she's qualified to do the business he's in, AND her husband is best mates with him... You can sort of see why she'd be tempted. What would you do if the boot was on the other foot?
That said, I can TOTALLY see why you're upset, and don't feel you can be around her. I wouldn't be able to either, and I'd also feel hugely hurt that my best friend 'chose' my ex over me... And if it were me in this situation, being offered the job, I'd like to think I'm a good enough friend to my mates to say no...
Basically, I don't know what the 'right' answer is, but my gut tells me she's sort of sold out on you, which makes her a not very nice person...
On the other hand, if it was a career opportunity not to be missed at any cost...
It's a nice view from the fence here!