How to define a sense of bitter satisfaction (or ironic bitterness) at having resigned over a principle - which was then upheld after you left

Tracey Crouch, UK Sports Minister, resigned because the government delayed a ban on gambling machines. More than a week after her resignation, the government changed its position - and acted upon her earlier insistence. Is there a phrase to encapsulate her situation and sentiment? A sort of inverted schadenfreude...?

The phrase cold comfort seems apt to describe her state of mind, but doesn't quite capture the ironical nature of the situation.

The sentence you provided could be worded:

Tracey Crouch, UK Sports Minister, resigned because the government delayed a ban on gambling machines. More than a week after her resignation, the government changed its position and delivered poetic justice: by acting upon her earlier insistence.

poetic justice OED

(b) (now more generally) the fact of experiencing a fitting or deserved retribution for one's actions; an outcome in which virtue
triumphs over vice (often ironically)

When good is rewarded with luck or a happy ending — or doing something bad results in punishment, it's poetic justice.

A recent sentence:

“I thought that was a little bit of poetic justice, if you will,” Coach Barry Trotz said, “for all the tough times.” Washington Post Jun 1, 2018