Pumpkin,
I just researched Madopar. It is a combination of benserazide (which I had never heard of before) and levodopa. It is known as Prolopa in Canada. It is not available in the United States. Since I live in the U.S., I can't address your questions about Madopar and of combining it with Requip.
However, I can address your questions about Requip which I have taken since 2001. (I am in my 50's shhhhhhhh). Requip is a dopamine agonist. It is often one of the earlier medications prescribed to people with Parkinson's disease (PD). It is the only PD medication I have taken (with a couple of brief additions of low doses of other meds). Normal dosages are 9-24 mg per day, although I've recently heard of folks taking more than 24. It is available in a formula taken 3 times per day or a formula taken once a day. You should titrate up/down of Requip (don't quit cold turkey).
The most common side effects are drowsiness and compulsiveness. The formula taken 3 x per day tends to have drowsiness associated with each medication time. The once-a-day seems to have less drowsiness. As mentioned, it is a dopamine agonist. The agonists (which includes Mirapex) can sometimes cause gambling and sexual compulsiveness. Sometimes there are other forms of compulsiveness such as shopping/spending.
If your Mother is not noticing any difference with Requip, she may need a higher dosage. I don't think it really does much until you are taking at least 6 mg/day (my opinion). You ask about replacing Madopar with Requip. Madopar contains levodopa. Another medication, Sinemet, also contains levodopa. People take Sinemet and also take Requip. It seems that once folks take Sinemet (or Stalevo), they never go back. Levodopa is one of, if not the, most effective medication (at least in the U.S.) for PD. Anything (legal) is worth trying since different folks with PD can respond differently to the same meds. No two people are the same - not with symptoms and not with treatment/meds.
Lastly, you mention your Mother sees a geriatric doc. Is that the only PD-related doc she sees? If so, I would suggest seeking a neurologist, or better yet, a neurologist who specializes in PD called a Movement Disorder Specialist or MDS.
Enough. Hope some of this helps and I hope folks familiar with Madopar will respond.
Best of luck!
lizzy4451