What should a committed girl do if she dislikes visiting her less-committed relatives and is forced to attend their events that violate Sharia, causing her great sadness?

The first thing you are advised to do is to supplicate for guidance and righteousness for these relatives, then invite them to goodness and strive to influence them if you are certain that they will not influence you negatively. Maintaining kinship ties (silat al-rahim) is obligatory, but if you fear corruption by visiting them, there is no sin in refraining and sufficing with other means of connection. You are not obliged to obey your mother in visiting them if it leads to disobedience [to Allah]. As for occasions that involve forbidden acts, it is not permissible to attend them, unless it is possible to stay away from the place where the forbidden act is occurring. You should always be mindful of the vastness of Allah's mercy and not despair of it.