In the name of Allah the possessor of the Most Beautiful Names
The name Arwa you have kept for your daughter is permissible and allowed in Islam. After consulting Sheik Umair Malik, an Arab colleague of mine I was told that it is a common name amongst the Arabs and is permissible is Islam. It was the name of Rasullulah aunt as you have correctly said. It translates to mean either "mountain Gazelle" or "very thirst quenching".
Just because a name has pre-Islamic origins does not mean that is it prohibited or disliked to keep that particular name after the instigation of Islam. Even the names such as Umar, Ali were pre-Islamic but they are the names of the successors of Rasullulah and are permissible to keep in Islam. If there was a name which was disliked in Islam Rasullulah would have changed it. The name Arwa does not go against any of the Islamic beliefs and is not a name which implies shirk (polytheism) of any sort.
Furthermore, your intention was that you named her after the beloved aunt of the leader of all humanity. This was noble and virtuous of you to do. In conclusion there is nothing wrong with the name you have chosen for you daughter, and do not be concerned about any further. It is permissible in Islam without any Karahat (dislike).
May Allah accept your daughter, Arwa for the work of His Deen and make her entry into Jannah (paradise) tranquil and easy, Ameen.
And Allah knows best
Sahih Al-Muslim Vol 2
Qamoosul Wahid Vol.2 Pg 1075
14th Oct 2005