If you're looking for Welsh language poetry, my favourite poet by far is Hedd Wyn. He was a poet during the First World War, which was naturally a big inspiration behind his work.
He's one of the most (if not the most) famous poets in the Welsh language, so I'm sure your partner will have come across his work if they have any anthologies or collections of Welsh poetry. His entire output was apparently published into a book entitled 'Hedd Wyn: Ei Farddoniaeth' (Hedd Wyn: His Poetry) in 2012, which I can't find in stock anywhere online but there's an amazon page here if you're interested. Otherwise I have a copy of a collection of his called 'Cerddi'r Bugail' (Songs of the Shepherd) which, while it's not this exact edition, I can wholeheartedly recommend!
His work is extremely emotional - as a Christian he was a conscientious objector in the war, but was conscripted against his will and killed in service at the Battle of Ypres. All of his writing is beautiful, but one of his most famous poems is 'Rhyfel' ('War'), which opens Cerddi'r Bugail with a haunting portrayal of the horrors he experienced. If your partner is into Welsh poetry I'm sure they'll have (or will soon!) come across him at some point; he's an amazing figure in Welsh history as well as an incredibly talented poet who's definitely worth getting into!