As a new nurse who was hired directly to an ED, my advice is always to try to get a practicum in an ED. If you can get a practicum in an ED you want to work in, that's even better. The ONLY reason I was hired to my ED is because I spent six months there as a student and busted my butt to make a good impression.
Since that does not seem to be an option, I would look for new grad residencies in your area that hire people to the ED. If this option isn't available, then think about ways your prior clinical experiences can help you in the ED. Understanding, even on a lower level, aspects of ICU care and OB can be beneficial in the ED as you have no idea what is going to walk through the door. Think of how you can present these experiences to an interviewer in a way that conveys that you can apply this knowledge to the ED setting.
At the end of the day, also prepare to not get an ED job right out of the gate. Look at where other new grads are being hired in your area, look at how those opportunities can prepare you for working in the ED in the future. It may be discouraging to not get an ED job right from the start, but you have a long career ahead of you and plenty of time to find your niche, even if the path doesn't seem "ideal" right now.
As far as being upset about the OB rotation, you are allowed to feel upset or discouraged, but you need to still go into every one of those clinical days striving to learn all you can and being thankful that you have a clinical site to go to, if that makes sense.