Well, now you have reason to look over her fence - because you were "worried she might be looking for something of hers, like a frisbee, and you would love to help her find it" - but, then you have a great view of HER yard! Maybe with your phone in camera mode filming a little video...
After reading this thread I agree that she is possibly laying the foundation for something. Might be as simple as getting rid of your chickens. Might be as big as trying to get money from your HO Insurance for health bills as another mentioned. Might be that she is just bored and figuring out her endgame still.
Had a friend that lived in a cul-de-sac. No chickens btw. Neighbor for some reason got a bit weird after a few years. This and that...stupid stuff, both had kids growing up at the same time (but weird neighbor's kids were a bit younger than friend's kids). Ended up that our friend put a non-working video camera in their 2nd floor window that neighbor could see. This camera was focused on the fence between the yards, and there was no way it could have seen into their house as there were no windows on that side and most of their backyard was out of view of the camera. Neighbor did not know it was not working, but apparently did cause them to take their issues down a few notches. In the end, they had to go to the courthouse to basically have the neighbors be told to behave and the weird neighbors had the legal right to x,y,z...but could NOT do a,b,c. Through the whole ordeal, our friends documented everything and may have been in communication with a lawyer throughout. However, the one incident that stands out to me (from their retelling of the issues) is this one: shorter fence (that can be leaned over) is between the two backyards. There are short bushes on weird neighbor side. Weird neighbor comes out with large pruning shears to trim bushes, but *oops* accidentally drops them on other side of fence while friend husband is doing yard work in the backyard. So weird neighbor asks for him to give the large shears back to her. Friend Husband ignores her, and does not get the shears etc. Weird neighbor is being theatrical, really trying to get him to give her the shears. Weird neighbor has already been told (by that above person at courthouse) they cannot enter the neighbor yard ever, neither front yard (no fence) or backyard (fenced). In the end, shears stayed in friend yard. Our friends are pretty sure that neighbor was likely filming this - there is a strong likelihood that handing large pruning shears over the fence could possibly look like friend neighbor was attacking her, giving her a basis for suing. Conclusion of that soap opera: our friends moved to a different home in a different neighborhood in a different county.
Anyway, be careful because your neighbor has gone through a lot of effort to make a foundation for something. Never once interacted with you over *years* until now - there is a reason, even if it is just simply that she is experiencing some imbalance or as complex as ulterior motives.