I hope that whatever your decision is, you make it for yourself and not out of concern or consideration for the hospital, the unit, or the manager. You'll be 1.5 years out of nursing school if you wait until 3 months postpartum to start a new gig, right? That is less than ideal. Sure, L&D is kind of a small world, but it is not that small. And it's not like your name & photo will go up on some 'wanted' website of piss poor orientees.
I worked with a woman who went through L&D residency with horrible N&V - needed a zofran pump. She called out frequently. She eventually had to take leave. She finished the 12 week residency, worked for a few weeks, and then circled back around to restart work a few months after her delivery. So, about a 6 month hiatus? She is still an OB RN after an abbreviated orientation once she returned.
You could always start the job. See how it goes. And call it quits a few weeks into orientation if need be. This happens anyways in many nursing realms with a steep learning curve....at least you have a good reason. Like you said, it's not even your dream unit, so you're not blowing your once-in-a-lifetime opportunity.
You know your extenuating circumstances (distance, tolls, high-risk status) that you have to weigh. Just make a decision for yourself, not out of concern for the hospital.
If they don't take you back, you'll have some experience and can explain your circumstances to the next OB hiring entity. If they're offended by your high-risk pregnancy and resulting circumstances, they are what's wrong with our maternal health care system.