SINEMET is the most widely prescribed and most effective drug for pd. It has been in use since I believe the 1970's and I wouldn't doubt over a million people use it and do very well in the first few years, many continue to function as they did before they were diagnosed because of sinemet and most dose up initially to 300mg or higher. Search this board for NAUSEA and you'll find very few posts about it. Everyone is different and there is a chance it might make your mother nauseous but the drug has a very short half life so it won't last long, maybe 1-2 hours and she can discuss alternatives with her doctor if nausea occurs. The drug companies have to warn you about every possible side affect to cover their liabilities, if you assumed you'd experience all the side affects in the aspirin package insert you wouldn't take aspirin.
Nausea and low blood pressure are 2 things to watch but I assume your mother has to take something and other parkinson's drugs also have side affects so you cope with side effects no matter what you take, your're putting neurotransmitters in your brain.
. My opinion is don't mess with MUCANA and the HINZ protocol for your mother, do you want to be responsible for having your mother take MUCANA which is a legume, you have no guarantee for purity or % active ingredient regardless of what your're told, it's grown overseas in INDIA, MEXICO, maybe china. Others on this board obviously disagree, just my opinion.

Keep in mind sinemet contains two drugs, levodopa which is a naturally occurring amino acid and cabidopa, which is similar in structure to levodopa and slows down the breakdown of levodopa in the peripheral tissues so more of it gets to the brain. it's the carbidopa which minimizes the nausea. So this is a simpler drug than some OTC drugs.

buy a used copy of THE PARKINSON'S DISEASE TREATMENT BOOK by AHLSKOG, great reference book with very detailed prescribing guidelines for deciding which drugs to take, how much, how to deal with problems like nausea, and when to increase doses, switch drugs, add drugs.
join a support group, contact local branch of APDA to find one.