Are you wearing it to bed or is it next to you on a bedside table?
I don't wear mine to bed so not an issue, I just have it on charge in our en-suite. But if it is flat down on a soft surface or piece of clothing it should prevent the light from showing.
Other option is buy her a nice blackout eye mask...we use them in our house...we are both medical and come and go at night so these help....

Divorce her

I'd tell her to keep her eyes closed and she won't have a problem.

Not sure if the 935 does this but in the battery settings on my fenix 6 I can turn the optical scanner off at night.

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"When the going gets weird, the weird turn pro."
Hunter S. Thompson

Ha! My wife has an optical HR sensor on her watch and it wakes me up too, but not too bad. If I were the husband here, I'd just shut if off. No big deal not logging HR/sleep data at night. In my life, that data isn't really very important anyways.

Are you sure it is the OHR, or is it the backlight turning on? (The backlight can be quite bright).

I can't see my OHR even in the pitch black - it's against my wrist. Perhaps tighten the band.

If it is the backlight - turn on Do Not Disturb overnight, this should stop the backlight coming on at random times due to gesture, or to alerts coming in on your phone. Also, try turning down the backlight intensity to 5%.

If this still doesn't work, take it off overnight - the OHR should shut down within about 5 seconds if it is motionless off your wrist.

Sure it's an option, but if my partner had an unnecessary gadget keeping me awake and she suggested I needed to wear an eye mask instead of her just turning the thing off, I'd think she was being more than a little ridiculous.

Getting good uninterrupted sleep, is infinitely more important than measuring it!

I used to have a similar problem with my wife's watch, I don't have this problem now with my ex-wife's watch.

"Well honey, now that you're awake..."

See how long that lasts.