The moment of success mixed with realisation of failure

Solution 1:

There is a word, although it is not that common; 'Blessedness'.

Blessedness: adjective

Source: Dictionary.com https://www.dictionary.com/browse/blessedness

"She had a moment of 'blessedness' as she realised what would have happened if she'd missed her snatch for the vase."

divinely or supremely favored; fortunate:
to be blessed with a strong, healthy body; blessed with an ability to find friends.
blissfully happy or contented.
bringing happiness and thankfulness:
the blessed assurance of a steady income.

The first word that sprang to my mind though was 'euphoria'. I realise this only relates to the pleasure of the success and does not intimate that the person is also blessed to have escaped misfortune too.

Solution 2:

I don't think there is one word that describes this sequence of elation and dread but "dread" would probably work as far as your sentence is concerned.

"She had a moment of dread as she realised what would have happened if she'd missed her snatch for the vase."