She would have to want it and be willing to risk getting back into a relationship with this Chuck guy. I (and others) see that her willingness to try this is a big leap of faith.
I am not going to waste space going over all the things that suggest that Sarah is getting her memories back slowly (actually more quickly when she is exposed to Chuck), that she feels "something" in 5.12, tears on the beach etc. I think there has been a great deal written about this, and clearly you don't find it to your satisfaction. That is your opinion (and choice) and that is fine. What we see as evidence you don't and I don't think that is going to change. Medcally this discussion would come under the "yes, but syndrome". Any individual observation can be refuted, but there are a number of observations that, when taken together, seem, to most of is it would appear, point towards one conclusion.