A perfectly correct, common, and literary form is „Noi nu ne cunoaștem bunica”, which is also easier to understand for English speakers. If I am a bastard (no pejorative intended) I will say ”Eu nu îmi cunosc tatăl” (nobody will say ”Eu nu îl cunosc pe tatăl meu”). These sentences have all the elements that appear in their English correspondent, and no more, tho in slightly different order. Yet, the sentence given by Duo is grammatically correct. Mind that the form I gave is not always possible. Or it is possible grammatically, but nobody will use it ever. Here it is possible due to the ”equivalence” ne=noastră, both forms are common, but if the sentence would be ”Noi nu o cunoaștem pe bunica aceea” (referring to an old woman we see on the street), practically nobody will say ”Noi nu cunoaștem acea bunică”, beside of some poetic or literary texts. However, all are correct, and you will be perfectly understood.
You never say "românescă" (which does not exist) for the language. "româneAscă" is the adjective for something (feminine, o tradiție românească ) which is typical from Romania. For the language you say : vorbesc românește sau franțuzește sau țigănește... (current language) The two other forms are more literary: vorbesc limba română sau vorbesc Romăna...
Lest there still be a little confusion or misapprehension, the o 'her' is not emphatic. It is what Linguists call a pronominal or pronoun trace. Spoken Rumanian increasingly redundantly marks the number, person, and gender of a direct object in a preverbal pronoun even when the noun direct object is present. See my earlier comment about languages differing in what they mark redundantly and what they don.t.
For those confused over the 'pe' -- many languages specially mark direct objects that are human or 'higher animate'. Spanish does this with 'a', so 1. Veo el libro. '[I]:see-1sg the book.' but 2. Veo al hombre. 'I see the man.', and for some Spanish speakers, Veo al oso. 'I see the bear. '
pero en castellano, no es siempre como Ud dice : veo AL hombre es una cosa y veo EL hombre es otra. Yo puedo muy bien decir VEO EL HOMBRE SENTADO EN LA MESA, pero dire VEO AL HOMBRE CORRIENDO EN LA CALLE, aunque muchos dirán VEO EL HOMBRE CORRIENDO EN LA CALLE. Depende mucho de que pais estamos hablando. Yo le estoy hablando de PERU y ECUADOR, aunque mismo entre estos dos vecinos, hay grandes diferencias de vocabulario y de manera de expresarse. MEXICO - COLOMBIA - ARGENTINA - CHILE es otra cosa también.Depende mucho también del grado de instrucción. de quien esta hablando. Ahora,el Rumano, con PE etc. nos esta complicando la vida. Pero es un idioma interesante.
The "o" here is the feminine third person singular object pronoun, "her" in English.. It looks like, in order to emphasize the object of the verb in Romanian, they repeat the object, here both as the pronoun "o" and as the noun "pe bunica noastră." We had this earlier when the sentence had both mă and pe mine.. I now know that the answer to my question above is that you need both "o" and "pe bunica noastră."
If I were to try a colloquial French translation of this sentence, i would say :" nous ne LA connaissons pas A notre grand-mere." and now that I think about it, it makes things easier for me to think that way. When I was a young boy, it was the way we were talking and my mother did not like it at all.