
I get where FL is coming from. I mean, after finding out that the medicine she's making is not working anymore for ML, you'd usually resort to other measures and it just so happened that the last resort was to pair him up with the saintess. Let's not forget that the reason why she knows the medicine is because she remembered the recipe. Not because she researched it.
Now, if the saintess didn't have feelings for ML, I bet they would have reached an agreement where the former would receive equivalent compensation for healing ML. But no, the saintess chose to use FL's feelings so that she can get ML, and that ended badly.
She wasn't following the original plot. She was just doing what she thought was best for him. No one likes seeing their loved ones suffer while helplessly watching from the side.
Hope she reaches a breakthrough with the medicine tho. So that FL won't have to rely on the saintess' power to heal ML.