Good start and good end. The middle needs more clarification though and was a bit too clunky to read smoothly. Perhaps using the buzzword of Nazi could enhance the engagement of introducing the protagonist. Here is an example:

When the daughter of a Nazi general falls in love …

Also, should the ‘falling in love’ become precipitated by a major event? Falling in love is not a single moment but rather a developmental process. Perhaps your logline could include the protagonist MEETING the Jewish boy – this event leading to their falling in love. This would read and function better perhaps than presenting a developmental process as a life changing major event.

Also, the action should remain focused on our protagonist. Sure the Jewish boy is struggling against the threat of being killed, but the focused threat is not this, it is the high stakes of the daughter rebelling against her father’s subscription to genocide that generates appeal and drama for this plot. So maybe use ‘she’ instead of ‘they’ before must. It’s a minor but important alteration.

Additionally, the closing action of your logline could be further enriched by what I’ve discussed in the previous paragraph. Perhaps the action is:

She must rebel against her father, assisting her lover and his family escape the train bound for Auschwitz.

Introducing an element a little more specific than simply helping them escape — like attempting to get them off a train — adds to the tension and stakes which you’ve already done a great job with when you established the primary character conflict of familial divide.So I love your concept, but perhaps something along these lines could achieve greater impact and engagement to your story.

When the daughter of a Nazi general falls in love with a Jew, she must rebel against her father to assist her lover and his family escape the train bound for Auschwitz.