| Quote #4
Lily smiled: she knew that Selden had always been kind to his dull cousin, and she had sometimes wondered why he wasted so much time in such an unremunerative manner. (1.8.15)
Selden does things without ulterior motives, unlike Lily.
| Quote #5
The fact that the money freed her temporarily from all minor obligations obscured her sense of the greater one it represented, and having never before known what it was to command so large a sum, she lingered delectably over the amusement of spending it. (1.10.2)
Lily's youth and naiveté is marked by her lack of foresight. Notice that she isn't immoral; it's just that morality isn't on her radar yet.
| Quote #6
The modern fastness appeared synonymous with immorality, and the mere idea of immorality was as offensive to Mrs. Peniston as a smell of cooking in the drawing-room: it was one of the conceptions her mind refused to admit. (1.11.83)
Compare Mrs. Peniston's reaction to immorality with Lily's when the latter is dealing with the charwoman's offer.