Is there a definite or indefinite article? Why is "the bag" incorrect?
it's correct, just submit that it should be accepted
It should have accepted both. (Swahili has no articles, so we might translate this as "the" or "a". )
Please report it next time, if the problem is still there.
Shouldn't "Mom needs a backpack" be correct? I will flag the suggested change.
Why is mother need her bag not right?
Because "mother need" is ungrammatical and because there is no possessive ("her") in the sentence. That would be "mfuko wake".