Red i am so sorry for your friend and her family, and as well as the grief that you are going through.
i find it really hard to "compare" late and early losses in terms of grief and understanding it. i think, down at the ground level - a mother and a father losing their child - the entity of the loss is the same. there is no baby in the end. the difference is that a late loss like that hits everybody harder and comes more of a surprise as the baby has been there for a while, also the slow-bonders usually manage to bond to it within 25 weeks, there's the bump, the kicks, it is all more real - which hurts more in one kind of way - but on the other hand it is way more acknowledged as a tragedy and less brushed off than an early loss, the couple or at least the mother gets way more support, as the news has already been broken and after those magical 12 weeks it seems that nothing can go wrong anymore (to someone who hasn't had losses).
i think you really CAN understand your friends grief - you lost a child, too, in the end.
late losses have the weight of all that time spent together, growing together, the perfect early scan pics, the heartbeat, the gender scan, the pics, the movements, all those memories...
early losses have the weight of never having had a chance to live even only that, to have very little to remind you of that baby. to have no monument, no gravestone, no sacred place where to go and grieve, and if you do make one for yourself, chances are you'll get some odd looks about it, while someone with a late loss won't.
late losses are more often met with dead silence, early ones are usually greeted with insensitive comments (i don't know what's worse, silence or "at so and so weeks it wasn't really a baby/what's there to be upset about/you're overreacting/" and of course, the magical "better early than later on" - whenever i heard that comment, all i could hear in my head was my own voice screaming "if you'd have to pick whether to spend 2 years or 5 years with your child, what would you fucking pick???").
maybe when approaching your friend, tell her that you don't know what it means to lose a child so far along, but that you do know how it feels to lose a child, the emptiness inside, how heart wrenching it is to be empty-handed at the EDD. that you don't want to compare your grieves and your situations as it makes no sense, but that it has been the toughest thing that you personally ever went through and that you're there for her.
and if she comes out with something insensitive towards your loss in those very first moments, try not to take it personally and forgive her as quick as you can. that amount of pain and grief can make even the most caring, understanding person lash out and launch venom around... and as much as it hurts and sucks, it is understandable in a way.
i'm sending you a massive massive hug
my heart goes out to your friend and to you as well