To me it sounds like she is actually saying: 'she writes under the letter' because the stress is on 'under'. Am I correct in thinking that? If so, where should the stress be otherwise?
The stress is on the particle 'under', because it is a particle-verb, which gets its specific meaning through the particle, in this case 'under'. Skriva under = sign (put your name on, to certify)
I should also say, IF the sentence is about her 'writing on the table under the letter' - then we stress first 'skriver' and I would probably also have a secondary stress on 'bordet', NO stress on 'under', but some stress on 'brevet' that is the last word in the sentence.
I assume these comments were about the old voice. Unfortunately the new voice incorrectly puts the emphasis on skriver.
I'd thought that didn't sound right, and checked the comments to find out. Thanks friswing for the confirmation.
Incidentally, in formal English documents you sometimes encounter the phrase "We, the undersigned, ..." to refer to the people who've signed it. (And the emphasis in that English word is on under.)