I don't know much about the series but I have read about Cersei's prophecy and how she's prophecized to die. And it just seems to me that Tyrion is a huge red herring in that regard. Jaime, albeit only by a few minutes, is her "little brother."
I agree with this. The relationship between Jaime and Cersei notably sours in A Feast for Crows
... and besides, prophecies are always more narratively interesting when characters tragically misread them (cf: Oedipus).
I also think that Cersei has misread - perhaps more obviously - the prophecy about being bested by a younger queen. She's convinced that this is Magaery Tyrell but it seems far more likely to be Daenerys Targaryen.
Petyr Baelish seems to be aware of this possibility as well, judging from his 'war of the three queens' quip.