But what if we were saying that he is not physically located to the west of her? Would it still be Níl sé taobh thiar di, or would it be something else? But would agree that without context that says otherwise, "behind" is far more likely what is meant here.
Also, can *Níl sé taobh thiar di." also me that he is not giving his support and/or approval to her?
The ao = í thing makes sense, but I found the ending consonant confusing; shouldn't the bh be broad? It sounded slender to me so I looked into it and I doubt I'm the only one confused. On teanglann.ie and the Connacht and Munster pronunciations are pretty similar to the one here:
For contrast, check this variant form, which should only differ by having a slender bh:
It sounds the same except there's no on-glide; so that means that in the first example it is in fact broad. But why does it sound like a /v/ instead of a /w/? The answer is that the dialects differ, and in particular Connacht Irish has two allophones of broad bh; from Wikipedia:
"/w/ (which can be written as ⟨bh⟩, ⟨mh⟩, or ⟨v⟩) has two basic allophones: the labiovelar approximant [w] and the velarized voiced labiodental fricative [vˠ]. The distribution of these allophones varies from dialect to dialect. In Munster, generally only [vˠ] is found, and in Ulster generally only [w] is found. In Connacht, [w] is found word-initially before vowels (e.g. bhfuil [wɪlʲ] 'is') and [vˠ] in other positions (e.g. naomh [n̪ˠiːvˠ] 'holy', fómhar [ˈfˠuːvˠəɾˠ] 'autumn', and bhrostaigh [ˈvˠɾˠɔsˠt̪ˠə] 'hurried')."
Edit: in retrospect, I should have realized that this is consistent with how "ubh" is pronounced.