@OP: Please post the options that your sister has.
To the ones asking which MBA they should do: please identify your target colleges first, until the I think there is no point in telling you which MBA to do as the number of specializations in MBA is as big as the ones for BA/MA, for eg., I have seen MBAs in Networking, System Administration, IT, etc just for technology related MBAs.
To all: You cannot choose anything if you have no idea what your career/life goals are. You can't just say "Should I do MBA in HR/Marketing/Finance or operations?" as the fields are very different, the jobs are different, growth is different, salaries are different, job security is different, etc. so knowing your career goals is vital. You just can't enter this thing blind.