It's true that she probably hasn't got much time left, three, maybe four years if we're lucky.
Would you go for the old dog you feel would fit (energy-wise) into your family, try to find a younger one or go for a puppy altogether?
She's currently healthy, but of course there's a good chance she won't be at some point. However, even with a younger dog you could end up with issues that lead to large vet bills...
Edit: Hey guys, thank you so much for your feedback, it's been very helpful - not to mention reassuring! \o/
I really enjoyed the stories about your pets (well, apart from the sad ones, of course, but thank you for sharing those as well!).
If nothing unexpected happens we'll likely take her home for a trial period between Christmas and New Years and see how we all get along.