Irene is incredibly powerful and we knew from the start that Erza should have been separated from Irene very early on in her life. The fact that someone as strong as Irene was not able to locate Erza despite her being quite famous in Ishgar, means she did not bother searching in the first place, ergo she doesn't really harbor any particular motherly feelings towards Erza. However that doesn't explain why they were separated in the first place, unless of course not only did she not love her, she might even have resented her to the point she wanted to kill her. In my fantasy someone cut Erza out of Irene to save the first and then fled. This were my initial thoughts when Irene for the first time was shown in the series.
Yes this is simply something I want to have happened just because I think it would be a cool background story for Erza. However since then we have learned that Irene originates from Ishgar. So if she wanted Erza back, it should not have been that hard to find her if she kept tabs on Ishgar. It's obvious though she did not do the latter. Frankly most of her behavior shows that even in the very best of cases, she's completely apathetic towards her own homeland and its destruction. There are also some strong indications she has unresolved love issues and in this chapter we learned she assumed that Erza was dead, but immediately after that she gives the order to kill her.
So a scenario starts to spin here of Irene having been dumped/betrayed by a guy she loved tremendously while she was pregnant with his child and to take revenge on him, or she simply didn't want to have anyone or anything related to him in the vicinity, she had the intention to kill the baby. The man in question then cut the baby out of Irene's belly (explaining that scar) to save it and then fled and when someone like that occurs, you have all the reasons to believe the child might have died as the chances are rather slim it could pull through all of that.
It's not so much a real theory as a scenario I would like to see being true.
