It's sounds like MIL has been terrific which is great and really what you need right now.
The anger is good oddly enough. It can be a huge source of energy to galvanise you into doing things and sorting things out.
I found the emotional ups and downs and unpredictability of when they hit to be the hardest thing. I felt deep grief where a howling gale seemed to blow through my body. This was when I could do nothing but sob and I didn't try and fight these - I just allowed myself to feel until it passed.
When the anger appeared it very much included anger at OW. I could never not be angry with her. I used the anger to get a lot done. I was the one who moved out of the main home (my choice and the right thing to do for me as we had another home and I wanted to live in that one) so had a lot of packing and stuff to do over several weekends so the anger really got me through that.
Hatred - god I felt seething pure hatred for XH and OW. It was part of the anger but quite distinct. Boy did I dream up evil scenarios for the two of them.
The sadness that just hits you when something reminds you of him can be brief if you have good distraction techniques in place. Sometimes it's good to wallow though and you do have to cry.
All of this is normal and is the nature of the emotional rollercoaster you're on. What matters is that you recognise that it's all part of the process and ride the anger to get things done!
Those moments when you have a lovely time doing nice things with DD and feeling normal probably seem fleeting now but they do get longer. The hours of grief, anger and hatred become fewer and one day you will be able to look at STBXH and wonder why you ever wanted to see him naked.
For the waking hours you need to get those coping mechanisms at the ready. What was your passion before you put DD and STBXH ahead of yourself? Was it reading, sketching, painting? I don't know one single woman who hasn't dropped a hobby or passion because kids and H's take a lot of time. So get back in touch with the old you and dig out the stuff in the loft (although the loft will be hard in other ways).
Walking is a great suggestion for the 6am wake up. There are loads of free apps which show you how far you've walked, pace etc. I use runtastic so maybe look at these?
You do need to be a bit Girl Scout with getting through these emotions and have your coping mechanisms all lined up but if really does help.
I can't tell you how helpful I found my thread on here though. It really gave me huge strength and some good laughs in the darkest of times. 