Is that Lab A and Lab B conjectural or actual?
There SHOULD be no difference in the cholesterol measurement from lab to lab. The agreed standard is currently
TC = LDL + HDL + (Triglycerides/5).
All are directly measured except the LDL which is obtained by jiggling the equation around. Even THAT can be measured directly by better labs (and soon all I predict.)
As far as what is safe , i.e, 130 for your mum, 150 for you, that depends on personal interpretation, age, sex, doctor, health (heart risks). Depending on who you talk to you might get a different value of "borderline."
Side effects of the meds are all over the "High Cholesterol" board... Just scan down and read for an hour or so...
Personally I'm a fan but the biggest complaint from people who don't like them is muscle and joint pain.
Liver should be checked periodically for enzymes (blood test) but the complaints in this direction are few.