There are not many narratives about Hazrat Umme Ummaarah’s (ra) death, but through different historical references it can be determined that she was alive till the time of Hazrat Umar (ra) and passed away during his Caliphate.1
1 Tadhkaar-e-Sahaabiyyaat by Talib al-Hashmi, ‘Hazrat Umm-e-Ummaarah (ra)’ p. 399, Published by Al-Badr Publications, Urdu Bazaar, Lahore.