i have the same pattern, morning dose works ok, noon less well. i think its a food problem. amino acids are actively absorbed in the small intestine and thru the BBB.
similar AA's will compete with l-dopa for active transport sites and slow down or even reduce absorption of l-dopa. remember, i think only 1% gets to the brain, the rest is broken down in the tissues.
stomach emptying may be a factor, i try to take my meds with 6oz of warm liquid and at least an hr after eating..
i take 100mg sin at 5:30am, 200mg cr at 7-8am, 100mg sin at noon, 200mg cr at 2.
your mother is older, you might want to take 1/2 cr at 2. i find i get best relief from a combination of regular and controlled release but cr is tricky for me, sometimes takes too long to kick in, sometimes i feel like i've taken too much. but i appreciate it's longer affect.

getting adequate carbidopa is important.
Studies show that the peripheral dopa decarboxylase is saturated by carbidopa at approximately 70 to 100 mg a day. Patients receiving less than this amount of carbidopa are more likely to experience nausea and vomiting.
http://www.medsafe.govt.nz/profs/Dat...Sinemettab.pdf

an egg has over 1 gram of tyrosine, you think you need supplements or we have a tyrosine deficiency?what is the limiting factor in dopamine production?

http://www.lucilleleader.com/l/congress.html