My dog is booked in for a spey in a couple of weeks but I am due to go away for a week 3.5 weeks later.
She is staying with a relative and his dogs. Will she be healed enough or should I put it off until I get back ?

Usually when the stitches come out after 10 days bitches are back firing on all cylinders; a few extra days lead-walking is often recommended recommended, but by 3½ weeks afterwards you won't know she'd had anything done.

Unless there is a problem with infection or something, she should be fine. I've had two spayed in the last month or two and the one who was routine I had a job stopping from charging around and jumping even just 24 hours later, the one who was pregnant and had pyometra took just 3 days to get back to normal, and both were completely healed in 2 weeks.