Are you familiar with computer engineering?
No but my daughter is a software engineer.
That's awesome.  Computer engineers integrate several fields of electrical engineering and computer science.  They develop computer hardware and software (like your daughter).
Please tell me the differences between system engineering and software engineering.
Computer engineers are involved in the hardware and software of computing (microprocessors, PC's, supercomputers, and circuit design). 
Which one is harder?
I believe they are equally difficult.  That's why students choose areas of in-depth study their junior and senior year.  Software is an area to choose.
Are there a lot of jobs available for computer engineers in the US?
Yes!  It's a huge field for this day and age.  Now, Computer engineers are focused on robotics research and more.