Oh my goodness, Kate, welcome to garden.org
I am from Vancouver originally and my brother lives in Coombs BC on your beautiful island there.
Those Southern Magnolia are evergreen here but do lose leaves sort of sporadically throughout the year. To be honest, I wouldn't prune any parts of it off where there are leaves right now. It needs all its leaves to continue recovering and growing and all the sun it can get. Once it's cooled off, days are shorter and the tree is more or less dormant would be the time to do a little pruning.
Could you possibly post a photo or two of your lucky orphan? That will help us to advise you how to prune when the time comes. The Little Gems stay pretty small so at 10ft. your tree may not get much taller, but it will happily get wider and bushier. They don't usually need much pruning at all.
I do hope you're planning how you will protect your lovely little magnolia tree through the winter? Did you plant it in a large pot or is it in the ground? I ask this because if it is in a pot you can then move it to a protected area for the winter months. I'm thinking it's probably not spindly because of neglect, it's probably been seriously set back by the winter weather.
In theory they are hardy in your zone, but . . this is a failing of the whole "zone system" because zone 8 up north where you are is completely different to zone 8 down here in the Deep South where these trees thrive. The reason is that your nights are many hours longer and your days are so much shorter there. So if the low temperature gets down to 30deg. F on a winter's night, well here it will be that low for maybe 2 hours but where you are it will stay cold for 6 to 8 hours. Also our ground temperature down here stays warm because our days are warm and sunny and longer in winter than yours. It's the difference between a plant freezing or not freezing.
