Bonjour !
When she came to my house, je mangeais.
"Came" is the past tense of "come"
so the "manger" has to be in a past tense as well ....
A- je mange = présent
B- je vais manger = futur proche (near future)
C- je mangeais = past tense --> imparfait de l'indicatif
D- je mangerais = conditionnel (I would eat)
Bonne année !!