It said her child was Clartes’ which she hid from the man who raped her. She just pretended that Wellmy was his.
Like the other person said, Wellmy was born out of love between her mother and her father, Clartes (of the ducal house). The mother was already pregnant when she was raped, but she didn't know until Wellmy was born (because of her vermilion eyes, which were the same as Clartes' own). To protect Wellmy, she lied about her heritage and started to plan her revenge on her rapist.
I also wish her ex-husband and first love, Clartes, would come to get her from the convent eventually. They need to talk. ╥﹏╥
That woman may have done terrible things but she was in a life she didn't want having to raise the child from her rape. I would have gone crazy too in her place. I hope she finds her love and lives happily