I recognized her but couldn't place her name. Grok nailed it.

U.S. Representative Kat Cammack (Republican, Florida's 3rd congressional district). She matches your description exactly: a Republican congresswoman who deliberately sat on the Democratic side of the House chamber (up front, near the Supreme Court justices section) during President Trump's February 24, 2026, State of the Union address. She wore a bright red dress and stood/clapped enthusiastically and repeatedly for Trump's remarks, while most Democrats around her stayed seated or protested.

Multiple viewers, social media threads, and live reaction posts specifically called her out as "the woman in the red dress on the Dem side who's the only one standing and clapping." Cammack posted about it herself afterward, noting something along the lines of sitting among her Democratic colleagues as they chose to protest/sit out. She's a vocal Trump ally and House Republican (on committees like Energy & Commerce and Agriculture), which aligns with your sense that she "works with or for Trump"—she's not a White House staffer, but a strong supporter in Congress who often backs his agenda.

This stood out in real time because it created a clear visual contrast amid the partisan split (many Dems boycotted, heckled, or refused to applaud on things like the economy, Olympians, etc.). No other prominent red-dress attendee (like honored guests Erika Kirk or others) fits the "sitting in the Democrat's area + kept standing/clapping" details.