[Mithalwen]

Elfhelm from the evidence of UT is a pragmatist and read the situation most accurately at the Fords. He does not seem to be the type to be swayed by sentiment or to be a slave to orders when it contradicted his judgement.. he followed Theodred's summons s bypassing the King.

I find Elfhelm one of the fascinating minor characters .. you can get quite a vivid picture from quite a little.

Clearly Elfhelm and Eowyn would have known each other well. He had been marshal (Though not Marshal of the Mark) at Edoras since 3012 when Eowyn was sixteen. With her Uncle increasingly under the malign influence of Saruman via Grima, and her cousin and brother based at Helms Deep and Aldburg respectively as the strongholds of their Marks, it is quite likely that Elfhelm was a confidant and perhaps protector from the unwelcome attentions of Wormtongue.

We know that Erkenbrand was left in military command of Rohan because he was an older man of dignity and authority. Grimbold was his nephew and there seems to be a parity between him and Elfhelm - Elfhelm doens not override him at the Fords, Grimbold does not assume control of the forces of Edoras. If you work on the basis that Erkenbrand was an approximate contemporary of Theoden and Elfhelm a generation younger then they are likely to be mid thirties to mid forties - contemporaries of Theodred which may be why when Grima spread his poison they were inclined to follow his lead rather than his father's. I would think it unlikely that one not of the blood royal would rise to the rank of Marshal much before 30 no matter how able they were so that ties in with the date that Elfhelm took up his post at Edoras.

I have a theory - though not one I can prove that Elfhelm may have been a kinsman of Theodred on his mother's side, The Rohirrim tend to have similar names in their families and since Hild was the sister of Helm I just wondered if Elfhelm might be kin to Elfhild... Not necessarily brother ..if he were the king's brother in law it would surely be mentioned, maybe a cousin. A fanciful idea I know but not totally implausible. In the structure of the story he would then be a kind of foil for Imrahil (another of my beloved minor characters).

To belatedly get back to the point. I think Elfhelm was astute enough to know that what might befall Eowyn at home could be as bad or worse than a battlefield . Maybe he knew she would find a way anyway and so the best thing would be to have her where he could keep an eye on her. Maybe he had some premonition - a disobedience but like so many a necessary one for the eventual success of the quest.