Maybe you could take her aside and apprise her of the situation. Let her know that he will handle it, and let her know that he's embarassed, so if she notices anything, she should pretend she didn't see it. Or maybe suggest that she wake him up in the morning and then leave the area of his bedroom/bathroom so he can clean himself up in privacy if need be.
He doesn't have anything to be embarassed of though. Let him know that it's not his fault and he doesn't have any control over it. My son was almost in tears embarassed by his bedwetting (resolved by age 8) until I let him know that I wasn't blaming him and we were going to work together to find a solution.
That being said, a lot of kids (boys mostly) that are still wetting at night at your son's age are doing so because of an underlying deep-sleep disorder. I would ask your doctor for a referral to a sleep study for your son. If he does have a deep-sleep disorder it could also be causing sleep apnea which is a little more dangerous than wetting. It's certainly something to look into anyways if you haven't already. And in the meantime, ask your local hospital if you can buy a couple of the fabric chux pads from them (the pads that are waterproof on one side and cotton on the other that they use to help with moving immobile patients) or try making your own if you sew. We have several of these and they were lifesavers until my son stopped wetting. He'd sleep with one under him every night (cotton side up so it's comfy) so we were only washing those small pads every day instead of all of his bedding.
Best of luck!
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Edit: Sorry to edit so quickly but I just saw the post before mine and I wanted to add that while the Desmpressin nasal spray does work for a lot of kids, it doesn't work for them all. We tried it with my son and that wasn't his problem. The spray is an anti-diuretic which means it forces the body to retain fluids instead of dumping them through the kidneys and into the bladder. This is not every child's problem. My son for example, was still running for the bathroom at the last minute during the day and was a very deep sleeper. His body just had not developed enough in that one particular arena yet to notify him that he needed to go until the last minute. Of course you combine that with the fact that he sleeps like the dead and he just wasn't waking up fast enough to get to the bathroom. He doesn't sleep so deeply any more and his body is more developed now so the problem is resolved.
Just wanted to let you know that there are several different causes of wetting. Find what works for your son.