My husband (and I) have also been on statins for more than 25 years. My husband kept his total cholesterol and LDL low - at the optimal recommended level of 70. Unfortunately, we did not know that he inherited a Lipoprotein(a) which is very atherogenic. Primary care doctors and even cardiologists did not test for it in the past either because they knew there was no specific treatment or they did not know about it at all - it was not commonly discussed.
My husband now keeps his LDL at 55 or lower and is taking a PSKC9 medication that has reduced his lipoprotein(a) by one third -- still way above the desired value but better than before.
There are several effective drugs in clinical trials but they are placebo controlled and my "read" is that you cannot take these other meds that might reduce your risk if you participate in these trials.
This might be the situation with your sister in law, who has blockages all over. I suspect it is -- either than or she may be taking a statin that is not effective for her but which may come with fewer side effects.