Can her job ask my wife to quit? (12 weeks pregnant)?

My wife has been absent from work for almost 2 weeks now. She is 12 weeks pregnant and in a lot of pain due to some muscle/ligament inflammation. We have been back and forth to the ER 4 times (tried 3 different hospitals) they ruled out gall balder stones, pancreas, liver, air in the lung, blood clot in the lung, etc. She got a CT scan because doctors were really worried she might have developed a blood clot in her lung. So right now she is home taking Tylenol to ease the pain. She was supposed to come back to work on Thursday, but she was feeling awful between her nausea, the upper right abdomen pain, so she called her job to let them know she wasn't going to make it that day. Their answer was, that if she was going to continue like that, she would have to present a resignation letter, and that she can come back to work after she gave birth. Can they do that? She is been at that job for 8 months now. Is she able to collect medical leave or anything related to that? Times are really tough for us right now, and now this. I really don't know how I'm going to be able to survive with a baby on the way, and being the only source of income. Please help me out.