Even if that would be the case, she would be of a completely different kind than those two subordinates of hers. For starters those two were objects infused with a personality and other magical properties, which then got dispelled when they were beaten. If Erza was similar, she should have been dispelled long ago.
Secondly we know a lot about Erza's history from the moment she was a little girl. So if she was the result of Irene's enchantment, why would Irene make a baby/child? And what's more why would she not care about it for all that time while Neinhart's reaction shows she definitely should be somewhat special as otherwise how could he have known her? I reckon he doesn't have a list of all the enchantments Irene might have made and would even less be afraid of them.
Thirdly those two subordinates didn't really look like Irene, while Erza has a strong resemblance to her.
So even assuming Erza is one of Irene's enchantments, it would be of a different kind than Heine and Juliet. Maybe some horcrux-like existence?