A currently viral video:
There are several different things that "talking backwards" might mean.
You might produce a vocalization BACKWARDS(X) which, when played backwards, would sound like X. That is, your vocalization would be a good imitation of a time-reversed version of some normal utterance X. Ian Catford was especially good at talking backwards in this sense. He practiced by playing audio tapes backwards — and demonstrated the correctness of his performances in the same way. There was a viral video on Youtube a couple of years ago that demonstrated this skill in a very striking way ("Reverse English", 11/1/2009).
Another possible meaning for "talking backwards" would be pronouncing the surface phonemic segments of a word or phrase in reverse order. Thus "clip" [klɪp] would come out as "pilk" [pɪlk], or "make" [mejk] would come out as [kjem].
But in fact, reversing the symbols is not at all the same thing as reversing the signal, and so a genuinely reverse-time version of "clip" would not sound anything like "pilk". Instead, the forward and backward versions would sound something like this (audio taken from the Merriam-Webster Online pronunciation of "clip", and reversed using the "Reverse" effect in Audacity):
And what Alyssa is doing is something else again. She's reversing the order of the letters in the standard English spelling of the word, and then saying something that represents how she thinks that letter sequence might be pronounced.
You can see the difference most clearly with the words that end in "silent e". Thus her reversed version of "garage" (pronounced to her as [gəˈrɐdʒ]) is [ˈɛ.gəˌræg]:
This is a plausible way to pronounce the English letter sequence
but it turns the "silent e" into the main stressed vowel of the word, pronounces the immediately preceding 'g' as [g] rather than [dʒ] or [ʒd], etc.
If we were actually to reverse the pronunciation she was given, again using the Reverse effect in Audacity, we'd get:
And if we were to reverse the surface phonemic sequence [gəˈrɐdʒ] we'd get something like [ˈʒdɐ.rəg], or maybe [ˈdʒɐ.rəg] if you believe that the final affricate should be treated as a unit (a sensible view that the powers-that-be in the IPA have apparently never been able to accept…).
But what Alyssa is doing, clearly, is thinking of the spelling, reversing the spelling in her mind's eye, and then pronouncing the string that results. Her facility in doing this is remarkable.