I think in this case, BS means "bull shit"

I suppose it means "bullshit".. :D It basically means "nonsense", though it's a rude word so I don't think you should use it.

In the United States, in an office situation, on a scale of 1 to 10, where 1 is perfectly acceptable polite language, and 10 could get you fired from a job, the word "bullshit" would be about a 3 or a 4, while the abbreviation "BS" (pronounced bee-ess) would be about a 2. Initials are sometimes in place of rude expressions to soften them. Some common ones are "SOB" (for "son-of-a-bitch,") "POS" (for "piece of shit,") "CYA" (for "cover your ass.") A "bureaucracy" means a big organization with complicated rules and procedures. "Bureaucratic BS" means complicated procedures that make someone angry because they seem unnecessary. "Could I borrow your Plexicon-2450 to do some tests?" "Strictly speaking I shouldn't lend it out without your filling out a departmental equipment loan authorization form and getting the VP of Engineering to sign it, but I trust you so I'll skip the bureaucratic BS. Just be sure you get it back to me by five today so I don't get in trouble."

BS is an abbreviation for 'bullshit'. Bullshit is counted as swearing and is deemed to be a rude way to say 'lies'. In this context it is probably used as the image being portrayed is a woman who doesn't care about other people's opinions. Tough as old boots! Tough to the point where she will use the word 'bullshit' without caring whether it offends anyone.