BS. Pre-professional training matters for a limited number of fields. Accounting, Engineering, Nursing, Teaching (if you need to be certified), Computer Software Programmer. There may be others.
For everything else, it's about charisma, warmth, being effective in written and verbal communication, knowing enough to be able to hold an interesting conversation, perhaps proficiency in a foreign language. If you have these skills, you will be attractive to people and they will want to work with you. Your older sister may be struggling to get her career off the ground, but I am guessing her choice of major is not what is to blame.