Translation:The dinner has not had the slightest effect on her.
I have obviously misunderstood something. I thought that with a noun beginning with a vowel you used uno, which is contracted into un' because of the initial vowel in the following word. Since this example has "un effetto" and not "un'effetto" and there are no comments regarding this, I am obviously confused. Is it only in front of certain vowels? Have I got it wrong altogether? :(
I have now figured out my mistake. 'Uno' isn't used in front of initial vowels, only before certain initial consonants or consonant combinations, so no need to drop the 'o' in 'uno' when it is used because it isn't followed by an initial vowel. Here, the noun doesn't start with one of those consonants or consonant combinations, so not 'uno'. So, obviously, un effetto makes perfect sense. :)