I'll admit I don't quite get it. If she had a child and the child's natural father wasn't married to her, isn't married to her, was married to her but isn't any more, and/or won't marry her, is she supposed to stay unmarried for the rest of her life?
Maybe you'll object that this isn't your point. But --- honest question -- what IS your point? Was she wrong to get married?
I'll let you play a little guessing game with yourself and decide which of these allow for the person in question to marry and which don't.
Now, per the social teaching of the Catholic Church the ideal situation is for children to be legitimately born into a family, and I assume you realize that extra-marital sex is a grave sin. It is most assuredly a sticky situation for someone to get knocked up by one person, and then go marry another. Thats not to say that such a situation cannot come about legitimately, but it is an irregular, discouragable situation. For Francis to make a big show pf specifically requesting to publically marry people in such in situation, especially without vocally reminding the faithful to conscientiously avoid getting themselves into such circumstances, is yet another instance in his long history of showing his contempt for the way things have been done and ought to be done. He cannot be ignorant of the message it sends for him to ostentatiously marry people in such an irregular situation (and put beach balls on altars, and declare "who am I to judge, etc). Its the message he wants to sent.