Hi OP, I'm so sorry for this incredibly difficult situation you find yourself and your DD in. Just the fact that you are thinking about these issues now shows what an amazing mum you are. I lost my DM pretty young (although a bit older than your DD), and sadly I experienced quite a few bereavements fairly early on in life. Here's what has and hasn't helped me, although each grief is unique and there's definitely no right or wrong in this process.
As some other PPs have mentioned, funerals are so important. I've come to believe they're not actually for the person that has passed away, but for the people that survive. I lost a relative who didn't want to have a funeral (in an attempt to try and protect us from the sadness and pain of that day) and it was actually quite devastating not to have a 'formal' outlet for our grief. The rituals of that day, as hard as they are, are such an important part of the grieving process. It'll be so important that your DD feels as involved as she wants/is able to be on that day.
My DF coped really badly with my DM passing, and it was as if his grief eclipsed everything else and there was literally no room for anyone else's grief. It was devastating, and exhausting, and our relationship has never recovered. He also moved on to another relationship very quickly, and that was incredibly devastating to me as he expected me to be very supportive and I just literally didn't have the emotional bandwidth to do so. I really wanted him to meet someone else and be happy again, just not within a couple of months, and not to ram it down it down my throat when I was still in the midst of my own grief. Cheryl Strayed writes really eloquently about how it feels to lose a parent at a young age, if you have the energy at the moment (I appreciate with everything going on you might not) I'd suggest you dip into some of her articles/books/podcasts if you can. Nigella Lawson and Joan Didion also both write eloquently on grief- their writings have been such a comfort to me over the years.
As I've got older I've seen my DM in a new perspective and I've so missed being about to talk to her with each of life's passing milestones- births, weddings, even other bereavements. It's so important that you keep talking to DD about DH if that's what she'd like. Especially the small incidental stuff. I can't tell you how precious these 'borrowed' memories from other people are. It seems impossible now but there will be a time you can reminisce and smile at a happy memory together, despite the sadness of the loss. My siblings and I are now able to talk about funny things my DM did back in the day and I'm so grateful that we can do that together.
So its a delicate balance of not overwhelming your daughter with your own grief, but feeling that she and you can both talk about your DH safely and are allowed to feel sad and grieve at your own pace. I'd suggest you line up separate grief counselling for you both with recommended professionals who specialise in grief and childhood grief. It might not help, and it might be the best thing ever, only you will both know when you get there, but it'll give you both a safe separate outlet, which is so vitally important when you'll both be desperate to support each other whilst processing your own grief.
I've hung onto a voicemail of someone I lost who was precious to me- and I really cherish it. I managed to record it as a voice memo on my mobile phone and then I emailed it to myself so I wouldn't lose it. Photos, notes, voice recordings, videos, belongings, and even an old jumper can all become so important when you're remembering someone you love who's gone. Only you and your DD will know what's important to you both at the time, but be open that it might not be a 'conventional' way of grieving, and that's ok. Also be aware you might both grieve in completely different ways on completely different timescales so be very gentle with you both.
Sorry, this has turned into such a rambling message. Please keep posting here, there's such an amazing wealth of collective wisdom on MN. Big hugs xx