To get the actual date of death, you will need to purchase the death cert.
To find a burial, you will need to know where and when she died - so will need a copy of the death cert!
The Registration District from the indexes will cover many many parishes, and the Qtr from the indexes covers 3 months, so would be very difficult for anyone to look for a burial without more detailed info, even if anyone did have access to the Parish Registers for Oxfordshire. Where was she last living - in 1881 - for example?