I'm not a handwriting expert but looking at the comparisons, especially the left hand sample, I can't find any substantive differences at all. They look identical. The only difference, perhaps, is that the ransom note looks a little more 'nervous' than the sample provided by PR.
Right...the only thing that gives me just a tad bit of pause on this part is this: If I think I am being accused of writing the RN and am asked to provide samples to the police and let's assume I did actually write the RN...I am pretty sure I could fudge a little on the samples so it wouldn't look the same - even with my non dominant hand...I don't know - wouldn't ya think?? Maybe she just didn't think of that?