The von Koch conjecture
Jelly, 30 bytes

JŒ!³,$€
Çµy⁴VIAµ€Q⁼$€TðḢịø³JŒ!


Try it online! (Use GṄ³çG as footer to make output prettier. )

Inputs similar to example, e.g. abcdef and [d,a],[a,b],[a,g],[b,c],[b,e],[e,f]

Outputs the list e.g. a,b,c,d,e,f in order.

Note: My program produces different values than the test cases as there are several possibilities which are all valid.

Explanation

JŒ!³,$€                - helper function, generates all possible numberings, input is e.g. 'abcd'
J                      - range(len(input)). e.g. [1,2,3,4]
 Œ!                    - all permutations of the range.
   ³,$                 - pair the input with ... 
      €                - each permutation. Sample element e.g. ['abcd',[3,1,2,4]]

Çµy⁴VIAµ€Q⁼$€TðḢịø³JŒ! - main dyadic link, input is e.g. 'abcd' and '[a,b],[b,c],[b,d]'
 µy                    - use a numbering as an element-wise mapping e.g. 'abcd'-&gt;[3,1,2,4]
   ⁴                   - apply this to the list of edges. e.g. '[3,1],[1,2],[1,4]'
    V                  - turn this into an internal list.
     IAµ€              - find absolute difference on each edge
         Q⁼            - Is this invariant under deduplication? Returns 1 if the numbering is valid; 0 otherwise.
Ç          $€          - apply this to all possible numberings
             Tð        - return the indices of all valid numberings
               Ḣ       - choose the first one and
                ị      - get the element corresponding to its index in 
                 ø³JŒ! - all possible numberings 


Save 1 byte by showing all possible solutions:

JŒ!³,$€
Çµy⁴VIAµ€Q⁼$€Tðịø³JŒ!


Try it online! (Use GṄ³çG⁷³G as a footer to make output prettier)

Use converter to copy-paste test case into an input list.