In my opinion, she's always been like that, RF. That's her face, although she may use botox (I have no idea), she hasn't changed much from Scent of a Woman.
I DO love her, she's the reason why I am enjoying this drama despite its admittedly slow pace. She's a natural actress, and while you are annoyed by her not expressing enough, I think she's expressing an incredible amount of emotions without retorting to the usual Ohhh and Ahhh of the typical rom-com actors.
In fact, I like the pace too.
This drama deals a lot with her internal struggle, and less with actual big events, but it's also the growth of a young man, and LJW (I copy, can't remember his name) is definitely doing a great job at it: he's indeed adorable, and if you have the patience you'll see more of him and more and more adorable. But, what can I say, you'll have to deal with KSA too, if you want him. :)
Uh, on a side note: she hasn't done anything to her lips. Not only her lips have always been like that, but you can see it clearly. Trout pout, or dinghy lips as we call them, are the result of filling, and let me assure you it's not the case of Kim Sun A.