At the end of the word "jenta", (at least my female robot voice did this, I don't know if this is how you would actually say it) you would hear a slightly enunciated "ah" sound. While at the end of the word "jente" the ending sound sounds more like an "uh" and is not enunciated. (I think)
Jenta is pronounced
/jɛntɑ/, while jente is pronounced
Pay attention to the presence of the indefinite article to help yourself in differentiating en/ei jente from jenta.
@TemShopper is right, the ə is similar to a diminished "uhhhh" sound that happens when you can't remember what to say next in a conversation, just like SpongeBob in this video.
This is optional. The feminine gender is completely optional in Norwegian and can always be replaced with the Masculine ending. In this case the feminine -a ending is used for the definite article, while -en would've been used if it was masculine. Both are equally correct.
Feminine: ei jente - jenta - jenter - jentene
Masculine: en jente - jenten - jenter - jentene
Jenta drikker vann. - The girl drinks water. [PS]
Jenta drikker vann. - The girl is drinking water. [PC]
There is only one present tense in Norwegian which can be translated, depending on the context, as Present Simple or Present Continuous in English. This means the app will treat both answers as correct.