Interference of PvP

That is certainly an option.  And I'm not crying foul over the attack.  I personally think it's a poor strategy to indiscriminately attack armies no matter where they are, particularly when PvP has been defined with specific limitations, but anytime one fields an army, stuff can happen.  Fortunes of war.

Since the only time I've ever attacked any player army is when 1) the army was sieging one of my alliance mates or 2) the army was counter-claiming on my sovereignty or 3) in a tournament or friendly competition, I can't imagine I'll have difficulty in not attacking armies you place near the cities of your friends.

See, that's where people misunderstand when they read fragments of other people's mail.

Here's the chain of events from Ryelle's perspective:

1)  I say to Juxwin "how's it going?"

2)  Juxwin says "OK, except fromfrak just creamed one of my armies, and she's complaining that I'm putting armies out around my cities to confuse this PvP thing"

3)  I say "That's most disconcerting that fromfrak would be attacking armies without scouting them.  I think I'll put an army out to see if it happens to me.  Where should I put it so as not to be in the way?"

4)  Juxwin responds with the mail you apparently received referencing where the action is taking place

5)  I send an army to check things out

My interest in this is not any PvP between you and jonazz.  My interest is in fromfrak attacking armies that are not involved in the PvP, which I verified that she was doing, and as indicated I suggested to her that she not do so again.

If I had as has been suggested been attempting to confuse things, it seems reasonable to expect that I'd send out more than one army.  A single army would not confuse even the most simple-minded.  It would only be a target if someone were indiscriminately attacking anything that popped up in an area.  Which apparently was the case.  So either you think that I think you're not very bright (which is far from the case, I have complimented you on your efforts in the past, for example in the tourney), or you are suggesting that I am not very competent, which is indeed quite possible but hopefully yet to be conclusively demonstrated.

1. The army wasn't placed as an innocent "observer" it was placed at the request of a third party to intentionally create confusion as to the target - I have shared the written request with Ryelle, and Ryelle acknowledges receiving it.

2. A blight shield was requested because my opponent had also been receiving a blight shield, and it was not understood to be a violation of the explicit rules of the PvP. In any case, the blight shield was cancelled and Ryelle said "it would be unethical for me to be involved" - so it is just doesn't make sense that

A. Ryelle's army was placed in the location as anything other than to create confusion as to whose army was whose; AND

B. Ryelle's belief that it's unethical for Ryelle to be involved, yet Ryelle gets involved.

In any case, I believe (hope) that Ryelle is no longer involved in the matter that is really not Ryelle's concern.

Ryelle was indeed willing to risk attack when she placed her army there.  The army was placed to verify whether indeed armies that did not belong to players directly involved were also subject to attack in that area.

That's why she did not retaliate in any way for the attack.  Instead, she merely noted the information and suggested that fromfrak be more careful about whose army she attacks in the future.

The suggestion that one army placed as an observer represents a substantial interference in anything is ludicrous.  I also note that fromfrak does not address her action in requesting a blight shield.