1) Going to college and studying what you are interested in is a very personal decision, and so if she wanted to major in English, strong advice against it from her older brother would likely fall on deaf ears. Besides, a degree in English is very practical. It's not like it's Art History or Women's Studies. There are LOTS of jobs out there for people with excellent communication skills, and a degree in English helps one acquire those.
2) Is she going to land her "dream" job within 2 weeks of graduating? Well, that depends on what her "dream" job is and how prepared she is to go get it. Did she have internships or paid positions in her field of choice while she was in college? Did she work her a$$ off to stand out among her fellow college graduates? I did BOTH of those things in college and so with a degree in journalism and English, I had a job as a newspaper reporter before I even graduated, and that was in 1989 with a tough job market.
For some reason, people like to rip on English majors. There are two sides to a degree in English; literature and writing. The literature side isn't going to help you in the working world too much unless you want to be a teacher or a professor or a few other niche areas. The WRITING though is extremely valuable. How many jobs out there say, "Excellent written and oral communication skills"? Oral communication comes with a little bit of practice, but the written takes a bit more for most people, and most people are horrible at it.
Also, there are some DREAM jobs out there for skilled writers and paths in place to get them. I know two people (both in their 20s) who are writers for television shows. They both started out as writing assistants working for peanuts and have now moved up a bit. Can be a very nice career for someone who loves that kind of thing.
Beyond that though, English majors are needed for EVERYTHING from Web development to marketing. If you are an average student though with average drive and average skills, be prepared for an average job.