Considering contractions would be part of the birthing process caused by hormones overall, probably still painful. I don't think her uterus realizes it's elastagirl on a hormonal level. Just because you know and can solve the issue doesn't mean your body stops freaking out
This is the unfortunate real answer.
It's like... Just because you have the ability to move your leg doesn't mean you can actually move it when you're having a cramp.
But like... We don't want real. We want funny.
You rained on our parade with so much placenta.
Are contractions inherently painful just because they're contractions though, or is it all the stretching that hurts? Because if it's the latter, contractions might just feel like a muscle twitch
"Pain during labor is caused by contractions of the muscles of the uterus and by pressure on the cervix. This pain can be felt as strong cramping in the abdomen, groin, and back, as well as an achy feeling."
The muscles are fully capable of performing the action. The contractions and spasms are the pain, as your body prepares them for what they need to do.
Besides, it's not actually the uterus that needs to contract, it's the cervix. And we have no way of knowing if elastagirl has manual control over her cervix. Most women don't have control over their cervix, hence why these contractions have to happen for childbirth to take place. It could also be risky to the fetus to try to stretch enough to make that happen.
I would assume the overall pain and discomfort would be very intense and would probably interfere with her ability to stretch. She does feel pain, y'know.