Difficult Broody to Break - need help!

I guess Aunt Inez is definitely one of those "broody" hens that routinely goes broody. She did it twice in the winter time, but locking her out of the coop for a day worked like a charm because of the cold. She went broody once again during the spring, but we decided we'd let her sit on some fertile eggs we bought. She hatched them out and was a wonderful little mama. So now the chicks are about two and a half months old, and she has decided to go for another round. We have tried just locking her out of the house during the day, but inevitable at night she goes right back to sitting in the nest box (much to the young chicks delight as they take the opportunity to cuddle up, even though they all can hardly fit) Last night we had some plastic easter eggs filled with water, then frozen waiting for her in the nesting boxes when it was bedtime. She seemed irritated, but decided to try and warm them up anyway. Today she's back to clucking, screeching, and growling outside of the coop door, annoyed that I let her sister in to lay, but refuse to let her follow. We really don't want to let her sit on eggs during the hot summer - it's an oven in the coop these days, but we're trying to avoid putting her in the dog crate because that seems like an easy target for the nightly possum visits. Does anyone have any other suggestions? We're going on about a week now. I thought about putting some egg shells in the nest box for tonight - do you think that could trick her? Also, does any one have any thoughts about the psychological effects of us keeping her from her imaginary eggs? She seems really upset that she can't get to her "eggs".