The betablocker does more than just lower blood pressure.
It is often prescribed after and infarct to avoid arhythmias.
For the bp, if she would take only one medicin, the dose would probably be higher, so that does not make so much difference.
It often takes a few weeks for the body to get used to the new medication. After those weeks, many side effects normally disappear.
The statin and plavix are not very clear to me.
Afaik, statins are not described to persons of your mother's age.
Plavix is a potent anticoagulation medication (blood thinner). It is normally decribed after placement of a foreign object in the bloodstream (stent).