No liaison between "et" and "une"

Bonjour Duo,
There are certain words in French where the liaison is omitted in the oral and this is one of those:
Forbidden liaison
Finally, certain liaisons are impossible:

1) after et ("and") - which allows it to be distinguished from est ("is") in speech.
2) after the silent final consonant of a singular common noun: coup X intéressant ("interesting deed"), rat X énorme ("enormous rat") - which allows a distinction between a noun and an adjective: un précieux‿insolent is a precious insolent person, while un précieux X insolent is an insolent member of the fr:préciosité literary movement.
3) after verbs with the second-person singular ending -es : tu manges X en paix ("you eat in peace"); the ending is elided instead.
4) before a word beginning with an "aspirated h": les X haricots (green beans), ils X halètent ("they are gasping"). (Note that even the so-called "aspirated h" is not actually pronounced in modern French.) In the regulated language, hiatus is required here. In everyday registers, this phenomenon is frequently omitted, especially with little-known words.
5) before certain words that start with vowels, such as onze ("eleven"), un when used to mean "one," and oui ("yes").
There are other rules of liaisons, i.e. obligatory liaison, optional liaison, etc.

J'espère que ma réponse vous aiderait.
Bonne chance et bonne continuation dans vos études en français, la langue de Molière et qui a été utilisé par le monde français depuis l’époque d’Hugues Capet