Don't know what to do ....

Hi All

My first ever poste here.

To be honest I'm absolutely heart broken and gutted but looks like I have no other options here.
To cut long story short (short - ish) my wife developed mental problems abot three years ago. It was a blow to our family and I've tried to support her and fight it as much as I could. It turned out that there is only so much I can do. After worst episodes calmed down and NHS crisis team hasn't been involved anymore our life became a disaster zone. Especially for our now 11 years old daughter.
Thing is that my wife's behaviour is often very strange but she doesn't want to accept it. In her head everything is my fault. Whats even worse every single effort from me to convince her to seek professional help is being treated by her as an insult and turned into personal atack on me.
She is not capable of keepeing any job, neglecting our place we're living in and struggling in any sort of longer interactions with other people. But since three years she refuses to accept it and go to see doctors. Some of her episodes became very hard to cope with. Not only because of her strange behaviour but also agression towards myself. Insulting me and my family is now my every day bread and butter. What's even worse my daughter is very often witnessing those moments and it breaks my heart to see her crying.
She also tried to speak with my wife about looking for professional help as even she can see she that it's clearly needed. Obviously with no effect.
Spoken to my wife's family in the hope of help but they have failed to convinced her too. Worst part of this situation is obviously fact that it affects our daughter. Never ending insults, screaming, strange behaviours while we're out etc. are something out of my wife's control and quite often happens with daughter being around.
Seeing no other options I will be looking for a divorce. I want to make sure that my daughter is living in a safe and peaceful place which is impossible at the moment.
Very scared to do that first step. Also feel very bad I must admit. I mean like someone who wants to leave wife while she is not well but trust me that is not the case. Nigthmare I have been experiencing for the last three years while trying to keep everything together (provide for family, dealing with my wifes episodes, seeing my daughter suffering etc.) must stop..

Now I want obviously my daughter to stay with me. Also if possible to stay in the place we're renting at the moment (school / my work near by). Not sure what to do and what to expect but I know I have to do it.
Can you please tell me a thing or two from your own experience / knowledge of subject that might help me ... ?
I will be very greateful for any sort of advice.

Many thanks