[Solved] Wife in denial about cocaine

Hello, I'm not a drug user and could do with some advice about my wife.
We have a 15 month old son (our first and planned) and have bought our dream home nine months ago.
We're everbody's perfect couple, ultra happy and she has just asked for a divorce overnight a few months ago and rewritten history, didn't want to get married eight years ago, hasn't 'fancied' me for seven years and that I have been controlling her through our whole 11-year relationship - which is ridiculous.
And, no, there isn't anybody else in the picture - although, we are still living together and she is out looking for her 'special love' every weekend. She is 35.
I found out a few weeks after these revelations that she has been doing coke when she is out drinking until 3am in the morning - and she is a big drinker on a night out.
She is challenging me to get her drug tested saying she hasn't done it since she left me, as she was only doing it as she felt trapped.
I have since learned that she has dabbled in the past (despite being anti-drugs vocally as she is a fitness instructor) and it has got worse since we have had our child. I believe she has had postnatal depression and this is how she is medicating it.
She says she isn't doing it, but two weekends ago she went out on a 12-hour bender on a Saturday and I saw her on Sunday morning in a right mess limping to work at 9am to teach her spin class.
At 4pm she was in the beer garden of another pub, completely OK and watching this band with a starry-eyed, almost adoring look on her face. She was then going up to everyone in the beer garden rubbing their hair and kneeling between their legs. And not for my benefit as she is emotionless towards me.
Later that evening she came to another bar I was at and one minute she was looking miserable outside the toilets, five minutes later she walks from the courtyard into the bar to push her way to the front of where a band is playing with her arms above her heard, with this weird, almost Jokerish grin on her face. Almost deranged looking.
Then she jumped up on a bench with three girls she didn't know and started dancing with and cuddling them all. Before talking to everyone in the crowd below. Then she is getting a drink at the bar and putting her arm round a complete stranger buying a drink and talking.
After she was outside pushing herself against a wall with the looney look on her face before being twirled round like a school girl.
She was having loads of intense conversations with strangers, then the next day she taught two classes in the morning after getting in at 2am, before trying to sleep on the sofa at 1pm. As she slept, her legs jumped around like electric shocks were going through them and her jaw was moving around.
The next weekend (I wasn't there) a friend told me she was spinning herself round a pole like a maniac on her own in a beer garden at 9pm one minute, then 20 minutes later her pals were consoling her like she was upset. A mate of mine who runs the club she was at later that night said she was in the toilets all night and had eyes like bowling [censored], and was stroking his belly (and she never talks to him).
She is in complete denial telling me she hasn't done any drugs for three months and has got her solicitor to challenge me to hair test her. But I'm sure she must still be doing it!
She has also lost a lot of weight (at least a stone), she gets away with it on her body as she is so toned, but her face is so skinny, her cheeks have lost all their plumpness and she has aged.
Any insight would be greatly appreciated as I am very worried about her and my boy!!!!!