The RN was stupid with a body in the house. Logically...
1) If the Rs did it together (or one covered for the other), they could have dumped the body somewhere and then produced a RN. Much cleaner and makes more sense to have the body away from the house like she really was kidnapped. If a neighbor saw a car leaving, they could say they were going to the bank to get the ransom. Since that easy scenario didn't happen, they must not have done it together.
2) If just John did it, he could have stashed the body in the trunk, found the note, told Patsy he's running to the bank and dump the body. Again it looks like a real kidnaping. That didn't happen either.
3) If Patsy did it, she knows she has no way to get rid of the body. She probably doesn't have ready access to as much cash as is needed for the ransom, so she doesn't have an excuse to drive off after the note is found. John would want to go to the bank and leave her with Burke. So she has to create an untruder and a murder that looks like a male sex crime.
However, they couldn't be going to get the Ransom between the time they got home on Christmas night and tne time they called 911. Nothing was open. Where would they be going?
I have always thought it was P acting alone. She didn't mean to kill her or mortally wound her, but once she did, she reacted as any true narcissist would. CYA. However, Patsy could not risk leaving the house. She could be seen, with no explanation or she could wake up John. I tend to think, at that point, she still thought she could con even John.
That RN has always just screamed Patsy to me. Regardless of the Handwriting. It's the content of the note. Over dramatic and over the top. Patsy in a nutshell.
The other thing you have to remember if RDI is that these are not career criminals. Patsy had no experience with murder. My guess is she never, ever admitted, even to herself, that she committed murder. It was, I would bet, a
"tragic accident". At any rate, it's pretty easy to wonder, nearly 20 years later, how she could have believed LE would not think a RN with a body in the house was extremely suspicious, but with her personality, I think she could easily have believed it at the time.