German is a heavily inflected language, like Latin. English has few inflections:
Sarah's house - the word Sarah changes to Sarah's to indicate 'possession'. In Latin and German, this 'case' is called the 'genitive'.
Man/men. The word man changes to men to indicate a plural
Television/televisions. The word television changes to televisions to indicate a plural
Sheep/sheep. Sheep is uninflected for the plural.
German has many more than our rather limited 2 or 3 inflections. For German, the word ending and (in some cases) the ending of the definite and indefinite article not only change to indicate plural or singular, or possession (genitive), which an English speaker is familiar with, but also for dative (the indirect object of the sentence) and accusative (the direct object of the sentence). Because of the German case system there are numerous ways to say 'the' in German: die, der, das, dem, des, den
Take a look at this website:
If you think your daughter can handle the German case system, then that's half the battle. I remember spending a number of break times at school trying to explain this to a girl who just didn't get it. Not only do you have to understand it, but you have to remember all the details, and then you need to apply it in writing, but harder still, in speech.
Both German and Spanish have simple spelling systems.
French and Spanish have a much closer structure than French and German.
French and Spanish word order are nearer to English word order than is German word order.
French and Spanish have many words in common - this can be either confusing (using the Spanish word instead of the French one), or helpful (being able to identify a word in Spanish because you recognise a similar one in French).
Hope some of this helps