Mother hen wont take care of her chicks

[ledbythelamb]

This is my first flock. I have 20 Speckled Sussex hens and two roosters that just turned a year old.
One hen went broody and hatched 5 chicks. 2 died (I think she accidentally stepped on them).
We put chicken wire around a quarter of the space in the large coop to keep the others away and give mom some space. She took care of the chicks for about 12 days and then decided she was through!
She kept flying over the wire, and when I patched it up she went nuts pacing so I finally took the fence down. Several times I caught her hoarding other hens eggs and trying to brood, and I'd take the eggs away and put her back with her babies, which she would ditch as soon as possible.
Mother Hen acts like she never hatched any babies and the chicks are wild and fending for themselves just fine.
Why did the mother hen just abandon them? I'm glad they are doing well on their own but I'm nervous about letting any more hens brood chicks if they aren't going to endure the toddler weeks

 

[DanEP]

Some chickens are good mothers and some aren't. I wouldn't let this chicken brood any more but your other girls may be great mothers unfortunately the only way to know is to let them try if they go broody. I had one buff orpington that would set on eggs for 2 weeks then quit but a white leghorn that was a great mother, you just never know.