Chalish,
Were do you get these ideas from?? Do you really think you can figure out how somone feels about there way of life from a short paragraph written by there sister?
The idea that you can “only feel happy if you are frum” is an untrue scare tactic used in all to many yeshivos, and can prove very harmfull when a person discovers that they could be machalal shabbos and not keep mitsvos and still be happy and fufilled,
besides for the moral issues involved it is just not a good idea to use proofs or other tactics that arnt true as this ruins the credibilty of the pepole who say them (if they are willing to lie or are deluded about this maybe they are about evreything else they saying so if somthing they say dosnt make complete sense to me why should i follow it ect.)