We don't know enough to say if she married Fréaláf Hildeson, tenth King of Rohan, and first King of the Second Line. We know that the rest of her family died during the war in combat with the Dunlandings. In context, I suspect that Fréaláf's wife may have been Gondorian given that Beren, Steward of Gondor was at Fréaláf's coronation, and there is precedent for a marriage between the House of Eorl. Éomer married Lothíriel, daughter of Prince Imrahil of Dol Amroth after the War of the Ring. His own grandmother, Morwen, Queen of Thengel, was of Numenorien descent, likely of the line of Prince Imrahil as well.
All that being said, a marriage between cousins of royal blood is not uncommon. Given that Fréaláf is the first of the Second Line of Kings he may marry Helm's unnamed daughter to strengthen his claim. I think the first is more likely, but it is still a possibility.
No really. It's in Appendix A of The Return of the King if I'm not mistaken. Page in and around 1040 in my edition.
You know, ten or fifteen years ago, I wouldn't have minded this at all. Before the proliferation of the Girl Boss tropes Action Women were dope as fuck. The Major. Trinity. The Bride. Jackie Brown. They're all good. Even if they're somewhat fabricated for an adapted story I didn't mind because they were well written and fit the story.
Now they're like toumors taking over the host story.