I think 'writing' groups can be tricky as every child will most likely be at different stages of writing. I think you have a few choices, you could either invite a few of her peers who you think are roughly at a similar stage of writing and work with them. You could make it quite formal or not depending on what your daughter wants. If they don't want any 'teaching' as such then I think its quite nice in a group context if they have some kind of overall purpose, which might be putting together a home ed style newspaper. You could just be there to help as and when they needed. A newspaper would mean they would naturally cover lots of different kinds of writing too, from writing reports to writing stories.
Or you could invite various ages/stages and give 'creative starters' where everyone writes at their own level. For example, you might watch a short animation and stop it before the end and then talk about what might happen next. Kids could write it if they wished or maybe those without those kind of skills could draw it out, perhaps as a cartoon. There's loads of ideas on this website:
www.literacyshed.com/
Its great, we have used loads of their ideas in the group I run.
Another idea would be to run the group with a different theme each time or each term. You could do a half term on poetry for example and look at a different kind of poem each week, for example, a shape poem or one using personification, and then they try to have a go themselves. You could go on a 'sound walk' and the kids jot down the sounds they hear and then put it into a poem......etc
Anyway the content of the group would most likely just evolve with the group & there are loads of resources on the net.
I would start small if you are new to the home ed community, you can always 'grow' the group ifs its successful. Start with just a small group in your home, 6 kids would be plenty. I tend to think writing is one of those things where kids like to feel 'safe' so small groups are good.
Once you have the children you can find out what they want to do. You could have activities up your sleeve, there are some fun writing games etc on this:
www.talk4writing.co.uk/resources/
If you want the whole thing to be a bit more 'free range' then you probably just need a range of pens/paper/stationary/postcards/nice letter writing paper/envelopes/paper folded and stapled into little books etc and maybe an ideas board were you stick a bunch of writing ideas each week in case they need more prompting. Then just let them go ahead and write!
Fun times! Enjoy! As long as everyone is having fun then the group is working:)