The sub q fluids are IV fluids that you administer just under the skin. If she is constipated she might be dehydrated enough to benefit from the fluids in addition to anything else you are trying. If you rub your finger along her gums, are her gums slick like a slippery piece or ice, or are they "tacky"?
If tacky, that is a good indicator that she needs more hydration and could benefit from the sub q fluids. Your vet can get you hooked up with a bag and teach you how to do it if you go this route. For me, the vet first gave fluids in the office, then sent me home with a bag for supplemental. I called up a vet clinic very close to my house and found that some of their techs do pet sitting. So I called one, and asked if she could come over instead of a pet sitting visit and help me learn to do sub q. It was a great way to learn. (PS - does Molly have a heart murmur? That might limit ability to receive fluids under the skin).