Dog waking us to go out at night.

Sounds like you all have lots going on. I expect in general the dog has a calming effect especially on your Grandson.
Spaniels and Poodles are quite intelligent breeds. They like attention and routine.
Inadvertently your DD has reinforced this behaviour by letting the dog out in the night.
Dogs are in tune with noise and movement so may think if it hears someone up in the night it is time to start the day or go out.
I’d agree a consistent phrase e.g. “ not time” or “lie down “ and stick to that for a few nights. Good luck.
If the dog is picking up on anxiety you could try a calming plug in for dogs in the room or a heartbeat toy available for puppies.

I too would put the dog's bed in a room with a floor that easily can be washed and refuse to let her out during the night.

Or alternatively, put her in a kennel in a dog run in the garden at nights.

I was waken at 4 a.m. by the cat who pretended that the lump he could see under the bedclothes was a rat.

As it was not, but his sister, she took the law into her own paws and asked if he wanted his bottom smacked and proceeded to do so. Strange to say, he hasn't caught anything in the bedroom at 4 a.m. since!

Your daughter certainly has a lot to deal with and I can fully understand why getting up to let the dog out at 2am is the last thing she needs. I have no advice other than to follow what ex-wife suggests. May take a few days but perhaps a tough stance may have the desired effect. Good luck .

My mothers dog went through a phase of doing that, I think it just became a routine for it. When I was dog sitting I simply said No and laid back down in bed, I had to this a few times the first night and once the second then he didn’t ask again.

I am not saying this is the case with your daughters dog but it is one of the reasons dogs do this.