I honestly do not see much trouble for females in EMS anymore. I haven't since the mid 80s, actually. There are jerks out there who do not like working with women, just like there are jerks out there who dislike working with other groups of people too. That's life. But it isn't a major factor in EMS as a whole these days. Although, your organisation may differ and turn out to be seriously misogynistic. You just never know.
If you run into problems getting along with someone, do not immediately jump to the conclusion that it is because you are female. Don't automatically be a victim. Find out the problem and work on fixing it. He may just not like rookies in general. He may not like people who went to the school you went to. He may have had an ex wife with hair like yours. You just never know. But most of the time, if you are willing to be the adult, you can work it out.
One problem I do often see with women entering the field is not at work, but at home. Especially women who have been married for awhile. And double especially if you have not been working up to this point. If you have been a stay-at-home mom for these years, and you suddenly are going to be spending a lot of time away from home, that is naturally going to cause resentment from your spouse. And EMS is generally much worse than any other job you could have taken because it involves long, unpredictable hours. Your husband is going to be coming home to a table with no dinner prepared on it, and clothes that never got washed, after you leading him to expect that for the last sixteen years. You are changing. You are breaking the deal. And this is often not well received by a spouse.
To compound the problem, n00bs to EMS -- unlike other jobs -- are generally way too gung ho about it and immerse themselves in the EMS "lifestyle", wearing their spouses out with stories that they have no interest in. And all that excited interest you show in your new career is excitement he wishes were reserved for him. So you can go on and on about it, and spend a lot of time at home wearing a uniform that he finds wholly unattractive on you, listening to the scanner all day long, and feed the resentment he feels for your new passion, or you can keep your mouth shut and feed the resentment you feel for him not being supportive. Either way, resentment grows, and so does unhappiness in the relationship. Seen it a thousand times.
So, how to avoid that? Simple. Remember this: EMS is not a lifestyle. It is not a hobby. It's not a calling. It is a job. Period. A low paying, lowly trained grunt job that most people have too much self respect to even consider. Don't think of it as anything more, because it is not. Don't wear it on your sleeve or the bumper of your car. Don't start buying "Third Watch" DVDs. Don't nail the "EMT Prayer" on the wall. Don't start looking for volunteer opportunities. Get up, go to work, put in your hours, go home, get out of the uniform, and be a wife and mother again. Off duty is off duty. If you feel that you need to put more time in effort into it than that, well you are right. But that time and effort should be spent on furthering your education to become a true medical professional. That is something your spouse can understand and respect, because he then knows that this is a professional commitment for you, and not just a new and exciting passion that is taking attention away from him.
Other than that, don't sweat it. This is the twenty-first century. Except in rare instances, real EMS is not a good ol' boys club anymore. You'll be just fine. Good luck!