How to stimulate my dog to poop

My dog is quite sick and has been on heavy painkillers since Wednesday. For the better part of the last three days, she has primarily been inside and I haven't noticed her pooping. She definitely hasn't done anything today.

I have given her milk of magnesia (her vet approved), and she's got an emergency appointment tomorrow morning but I'd really like to help her be a bit more comfortable tonight (she's panting quite a bit and is restless). I've tried the stomach massage method, the anus rubbing method, the spray bottle method and nothing is happening. I will give her more milk of magnesia in about two hours but is there anything else I can try in the meantime? Her stomach is HUGE.

@C thank you. As mentioned, I have discussed this with her vet but it is late at night now and still nothing is happening. If this app was JUST for parenting there wouldn't be different forums, including one for pets. Also as mentioned, she does have an emergency appointment tomorrow morning but I would like her to be more comfortable tonight.

@thanks all. She seems to have done some business overnight as she is a lot more comfortable. We are still going to our vet appointment this morning!

Also at C, I'm hardly asking for medical advice. I'm asking to stimulate poop. I'm not asking for ways to treat my dogs cancer or something like that. It's literal poop.