I wouldn't say she saved her. If the MC's father hadn't hidden her away then she could have easily been sentenced to death for the attempted murder of a saint. Heck, the only reason the crown prince was willing to pardon her later in the story is because he realized he wasn't able to do anything without her after she was gone. If she had been sentenced she would have been put to death before he realized just how much he needed her to succeed and she wouldn't have been pardoned in time. Also the saint didn't care if she lived or died. She wouldn't have stopped the MC from being put to death if it meant protecting herself and allowing her to be with the prince. That's obvious when the temple "tests her poison resitance".
That wasn't really my point though. I'm just happy to finally see a saintess who just wants the Prince because she loves him and not because she can be crown princess or queen. In other Stories the saintess gets med or dump the Prince when he is no longer first in line, decided to give up the crown or lose his status as Prince. This one just want to be with him because he is him
I'm confused on why you would have added that to your comment if it had nothing to do with the point you were making.
Finally a saintess who just really loves the crown prince and doesn't care about becoming queen. She just wants him. And who actually "saved" the MC by taking the poison that was meant for MC instead