Does Allah get angry with a girl who, in her heart, loved a male classmate without telling her family or speaking to him, and is that considered a sin that prevents the completion of her engagement?

It is not permissible for a Muslim to attach their heart to that which is unlawful for them. Perhaps the suitors' aversion is due to sins and attachment to a person whom it is unlawful to be attached to. Therefore, we advise you to repent to Allah, adhere to His obedience, and diligently observe the prescribed remembrances and supplications.