John,
I'm not in U.S. and we don't have sinemet er so can't comment on it but sinemet cr 200mg I can.
A few yrs back I found it caused more dyskinesias and was told by a new neuro it was probably due to the unpredictable on than what a normal 100mg would give so went back to that.
Soccertese makes a good point about being a suitable candidate for DBS if she finds little relief from Sinemet.
On the other hand if she is getting more symptomatic with less quality of life and can still find good relief (perhaps not as frequently but still good relief) at times through the day she may respond well with DBS.
Recently my neurostimulator batteries (IPG's) went flat and were changed however in the time (which was only days) before new IPG's were replaced I was reminded how grateful and how effective DBS is.
My symptoms without stimulation have advanced considerably and personally I'll be eternally grateful for the function it allows me.