"She eats bread and jam."
Translation:Elle mange du pain et de la confiture.
Before an uncountable noun, with the meaning of "some", you need a partitive article:
- du beurre, masculine singular, before a consonant
- de la confiture, feminine singular, before a consonant
- de l'oignon, masculine singular, before a vowel sound
- de l'eau, feminine singular, before a vowel sound
"Une tartine" is countable. With just "bread", we don't know that it is "une tartine" or "des tartines", but we know it is "du pain" (uncountable).
By the way, we don't know either if the jam was spread on the piece of bread, which is the first condition for a tartine, or if the bread and jam were eaten separately.
The hints can't tell you that, in isolation, "jam" translates to "de la confiture" because the meaning of "jam" in the context of the various sentences it is used in will change the determiner.
- Je cherche une confiture de fraise = I am looking for a strawberry jam: indefinite article
- Où est la confiture ? = Where is the jam?: definite article for specific things
- J'aime la confiture = I like (the) jam: definite article for generalized things/
- Elle mange du pain et de la confiture = She eats (some) bread and (some) jam: partitive article for "an unknown amount of a mass".