So, could Pun-Pun create a magic trap that casts Greater Celerity on her in response to a command word, and two magic traps that cast Greater Celerity on her each time Greater Celerity is cast within some defined area? The first one sets off a cascade, and the other two each trigger each other (since they can't trigger themselves, I think, even with an instantaneous automatic reset).
I don't think Pun-Pun can ever terminate the turn she takes as a consequence, but she
can jump forward by 1 round (via Timeless Step) each time she wants to advance time. Also, once she does this, she can splinter off clones who are not subject to the infinite turn, and who retain the infinite experience, etc.
EDIT: Hah, you're right. So she has
infinitenigh-infinite swift actions, by Divine Impetus. SUBEDIT: Which I now realize is in the OP. Herp a derp.
EDIT: Drat, that's not an available trigger. We'll have to get a bit more
Goldbergian - we need a trigger trap that casts mage hand on a lever, which triggers a trap that casts mage hand on a second lever that is the trigger for two traps (something we're never explicitly forbidden to do), the first of which casts Greater Celerity, and the second of which pulls the first lever again. The levers in question all have an instantaneous reset, and may be replaced by other triggers if you find infinitely-fast levers to be implausible.