1. I believe the surname would be spelled without an "a" after "Vit-". There are over 500 listings for ViTKauskas (including the unmarried female, Vitkauskaite and the married female Vitkauskiene) in the online phone book for Lithuania, but there are no listings for any one whose surname begins with "vitak-". While it is possible that Ona Vitkauskaite marred a man with the same surname, Mr. Vitkauskas, it would seem unlikely to me. If she married a Mr. Z^urauskas, her married name would be Ona (nee Vitkauskaite) Z^urauskiene. The surname Z^urauskas would be pronounced zhoo-RAUS-kas, not zoo-RAUS-kas.
2. Her death certificate may have useful information on it so if I were you I'd wait. Be aware, however, that what is on the death certificate other than physician-provided information is what the informant provided, i.e., whoever gave the non-medical information to the doctor or funeral home. This can be a source of poor or even incorrect information because it is provided by someone who knew the deceased and may or may not recall correct information. I have seen death certificates with significant errors about date and places of birth because the son or cousin could only give what they knew.