they met a first time in 1973 some years before their relationship (wich was from fall 78 to september 79)
the "trilogy" Romeo & Juliet - Love Over Gold - It never rains talks about her and their relationship.
indeed, Hand in hand and Solid rock contains also some hints about Mark's feelings regarding trhis story
even if "Where do you think you're going" was not written specially for her, when Mark sung it during the 79 fall, just after they broke up, the song had obviously a special flavour.
Paul Cumming talks about this in the Oldifield book. just before a gig (likely the Boston one on 8th september 79) Holly phoned Mark and said it was over. Cummins says that Mark sung this song on stage this evening like he never did before
I have a little theory (although not confirmed, just my imagination) : the neck lace that Mark wore in 79 could be a gift from her. Why am I thinking that ? because this neck lace appears on pictures in end 78, and disappears in autumn 79.
I summed up all these infos in my chronicle about "Romeo & Juliet" :
https://textes-blog-rock-n-roll.fr/une-chanson-a-la-loupe-romeo-and-juliet-de-dire-straits/it's in french, but with Deepl or Google, I guess you can get a good translation