I'm sure she was fine with it when you said you were going to get guineas. What she didn't expect was that she would also end up with guineas. She probably anticipated that they'd be around but not in her space all of the time. They aren't hers. If she'd have wanted some, she'd have gotten herself some. But now she has yours. And perhaps your guineas didn't really bite the grandkids, but she was afraid they might and exaggerated it a bit in the telling so that you would take her concerns more seriously. Obviously you didn't do anything the first time she asked, and she may have felt that stretching the truth a little was the only way she might get your attention. Fact is, anything or anyone threatening my grandkids better stand by because they are about to run into a buzz saw the likes of which they've never seen. Just because you haven't SEEN them bite at the children does not mean they haven't.There's an old saying, "The only person who doesn't hear the dog barking at 2 am is the owner of the dog." My grandkids don't have to be hurt for me to take action - if they are scared then that's all I need to know.
It's clear that you really wanted a natural way to rid your property of ticks. (Oooh I hate those things so much just typing the word gives me the weebies!) You don't want a hostile situation between you and your neighbor. Look, I see your points very well. I get that you don't want them confined in any way, But that's your problem to deal with and should not be hers. You took on that responsibility when you ordered them. You didn't see this coming, even knowing that they would be free ranging, simply because I'm sure you figured that with that much acreage they'd stay put. They didn't and your neighbor is unhappy about that. She has every right to be. I'd have already had the shotgun out if I'd informed a neighbor that his/her critters were encroaching on my property and they did nothing.
I've read your posts a couple of times and I still am not sure what you are asking here. Are you looking for help with your problem or validation of your opinion and folks in your corner against the neighbor? Suggestions have been given but since they aren't what you want to hear you seem to be getting a little defensive. We don't want that - we just want to try to help you keep your guineas and not have any more problems with the neighbor.
Dabbing a bit of color on them so she can identify the troublemakers seems like a very good idea - it lets her know that you are taking her concerns seriously, that you do want to fix the situation, and gives her the chance to be pro-active in the solution instead of just looking out the kitchen window and getting angry. Chicken wire is cheap and you could simply unroll it against your existing fence and zip-tie it place so they can't squirt out. You could put them in a larger version of a chicken tractor and move them from place to place on your property to keep right on doing what you want them to do - zap ticks. (Oooh there's that word again!)
Tuck your resentment into your pocket and let her see you are working on solutions instead of just getting irritated with her. As I said, if you lived next door to me, where to keep those guineas would no longer be an issue, so you've been lucky so far. Good luck with the entire situation. You seem to have a good head on your shoulders so if you start thinking with it instead of thinking with your irritation I'll bet this could be resolved very quickly. And by the way, they are are pretty birds!