According to the OFHS's Oxfordshire Marriage Index (1538-1837), both Elizabeth and Thomas were minors at the time of their marriage in 1795 - which would probably explain the need for a licence (although from the date you give for Elizabeth's birth - 1773 - this would make her around 22 years at the time of her marriage).

The actual Ambrosden register entry will give the names of witnesses and possibly other information.

Penny