When she lambs the spoon will pop out, no bother. You do not need to do anything.
When you reinsert the prolapse, she will pee as soon as the bladder entrance is clear. (Be ready for this and have your sleeves rolled well up!)
When fitting the spoon, she should still be peeing. Not constantly, but a bit now and again. If she can't pee, the spoon is in wrong. If she can pee the spoon is in right.
The most common problem is to not tie it in tight enough. As long as she can pee she will be perfectly comfortable, so make sure it's pulled hard up against the bottom of the vulva. If it's loose, she'll pop it out, closely followed by the prolapse again.