If you're wondering where is the Romanian word for "my", the answer is that it isn't needed. "Mama mea este istoric." is a valid sentence, but it is assumed anyway that the person in question is the speaker's mom. To be fair, this is also true in English. Maybe it's rare to see "Mother is a historian", but "Mom is a historian" seems perfectly natural.
"Mother is a historian" wasn't accepted. I agree that leaving out "my" with "mom" seems more natural than with "mother" - after all "mother" is also used by/for nuns - perhaps most notably mother Theresa, but still I think it's more or less globally understood that you are indeed referring to your own mother if you leave out "my". I'm not getting worked up about it though :). Cheers.
The "correct" answer shown was "mother is an historian." My translation, "Mother is a historian" (with "a" instead of "an") , was rejected, but should be accepted.
Many English people say "an historian" instead of "a historian" but this seems utterly wrong to me.
The "an" would make sense if people would say: "an 'istory" (dropping the H). In standard English, the "H" in "Historian" is not silent, so I claim that the word "a" is applicable.
My guess is that saying "an history" is a centuries-old relic of the historical language of power, French: with a French accent, the "H" would always be silent. In France, Hockey is Okay!
Not sure how to submit a correction to "My mother is AN historian". It comes up as having a typo if answered "My mother is A historian", however, in North American English this would be the correct phrase. The word AN is only used if the next word begins with a vowel, A is used if the word begins with a consonant. I have heard British people use AN before a word beginning with H, but this is not typically done in North America.