That's not true. Computer Science has equal opportunities for both men and women alike. You could get several instances where women are really doing so well in this field, be it in the Information Technology industry, academics or in research. So, do not worry and go ahead with your choice.
My area is actually computer science, not computer engineering. The two are completely distinct, separate departments and research areas, with some overlap but not much. So you will need to read up a bit on the two and learn about the differences. I must admit I don't know enough about CE to tell you how it differs from CS other than to say that it definitely does differ. For example, at USC CE is part of Electrical Engineering, while CS is a separate department.
First: you should say "many fewer job opportunities"; good writing is a major pre-requisite for success in any field, including engineering. Second, no, that's not so at all. Engineering careers are the highest paid today, and they are also the only ones these days that are hiring people in large numbers; engineering majors get jobs while others have more trouble, this is clear from all recent surveys and hiring/placement data analyses. Finally, it is not the case that women do not get jobs; women who are top students get more job offers than men do, because there are fewer women in the field, so top women are in high demand. So my advice to you is to go into engineering, find an area that you enjoy, and do as well as you can in it.
Your sister is wrong; she is not speaking from an informed point of view, one that is based on actual data, but instead is probably speaking based on anecdotal evidence (someone said something) or worse yet and more likely, from stereotypes. You need to make sure you get very good information and advice when making major life decisions. It's always important to talk to your family, but it is just as important to talk to people who have scientific data and evidence to back up their claims. In this case, your sister does not. She no doubt means well, but she is not correct, and that's good news for you and other women in engineering.
By the way, to avoid such confusion, it is best to get involved with your field of interest early, during high school or even sooner. Go to a local university and talk to students (and professors, if you can get their time); they will tell you what things are like. The next step is to volunteer your time in a research lab, to see what the work is really like. That will teach you more than anything else.
Best of luck!