It's just to bad he wasn't a stable boy.

That and the king because it would explain why she always said that love is weakness

No . Cora was always very ambitious and interested in being a queen and from the moment she couldn't be one she had to make her daughter a queen . Don't forget that she enchanted Snow's horse befor she knew about Daniel so it wasn't like she already knew and she was afraid that he would treat Regina the same she was treated . She just had a plan and she was willing to vanish everyone and everyything that would come as an obstacle.

It makes sense to me.

No offense to Daniel but he WAS a peasant quite like Jonathan, and Jonathan ended up tricking her so a part of her was probably worried for Regina.

It Does Make a lot of Sense to me as well

It might have played into her feelings somewhat, but I think I remember Cora was controlling Regina before she knew about Dan.

I hadn't thought about it but it does. It doesn't justify it but it totally explains it.

Marakii and SherlockStark have a point.

Cora was already planning on Regina marrying the king before she knew about Daniel. Daniel just threw a wrench in things, so she killed him. Cora just wanted Regina to do what she wanted her to do. She killed Daniel to manipulate and bend her daughter into doing what she had planned. And to show her that love is weakness.

Maybe....

No. Cora was never interested in protecting her daughter from heartbreak, she just wanted to live vicariously through Regina by making her queen. Daniel was simply an obstacle in her plan that she had to get rid of.