Women should know all they want to know about cars. The only reason that mechanics and overall car enthusism(sp?) is widely male dominated area is because of a few gender specific characteristics.(please take in mind that these are overall generalizations and no way apply to all)
1. Working on a car or anything that weighs 2+ tons, takes a lot of physical abbility. Most women I know don't have the overall physical makeup to lift, budge, beat, etc.. very heavy and bulky objects.
2. Changing your oil is a very dirty process as are many jobs on a car. Most women I know aren't the most willing to dive into gross oily/greasey/grimmy setting to fix something.
3. It is a very rare occasion that I come out from under my car without any scrapes, cuts, or bruises. Women usually don't want to be walking around with cuts all over their hands/arms.
I will say that women should be informed to the workings of a car and when service is required(I.E. read your car's manuel). Also, don't just go to any mechanic thats a buddy of the guy you work with. Call the better business bureau in your area and find out which mechanics/dealers are reputable and which ones aren't. Along with that get a few opinions when your car needs repair work, guranteed there are mechanics that will charge a women for unneccesary work just because they honestly don't know what needs to be fixed and how much it should cost. Lastly, if you think there is something wrong with your vehicle get it checked out by a qualified tech(ASE certified) ASAP! The longer you wait, the more it usually costs.
Hope this helps. -Peace