DD and I are already arguing about S1 subject choices
and she hasn't even started yet! We also dropped to 9 subjects at the end of S1. I think you are over thinking it this early on, save the arguments for school uniform, homework and revision! Wait until closer to the time, agree she needs to try the subjects at secondary school before thinking about what she enjoys/is good at.
Also be aware (in our school anyway) they constantly assess in S1 before the subject choices, this starts even in the first few weeks, they don't warn or expect study towards these assessments, they say they are assessing their natural ability. Your dd will not be aware these will determine in S2 what set for English/maths they are placed in and whether they are allowed to choose some subjects.
Some of ds's friends were not allowed to take physics or chemistry, they were told they were only allowed to take "general science" (biology seems to be seen as an easier science so sometimes allowed), you had to have shown aptitude in the assessments to be allowed to take physics and chemistry together. Some were told they weren't allowed 2 social subjects e.g. geography+history, or 2 languages etc because they didn't show a strong enough aptitude for the subjects.
Some were even strongly recommended/told to choose
an "Employability" option in one of the columns, which imo is basically saying we already don't expect you to stay beyond S4. So they are writing them off for highers just a few months into S1 based on assessments they didn't know mattered! 
We were lucky that ds(15) choose pretty standard subjects that were all available - English, Maths, French, Physics, Chemistry, Modern Studies and PE. Some friends had 3-4 of their choices vetoed either due to ability or told it was because classes were too popular/full.
Subject choice looks really crap compared to when we were at school
Same at our school. It is very school dependent (budget and having the subject teachers) what they offer.
A work colleague's children go to a Glasgow school and they have loads more options that ours, Computing Science, Engineering Science, German, Home Economics (or what ever the modern name is!), Psychology etc which ours just doesn't offer.
Ours also offer very few advanced higher subjects and the way the columns work out ds would only be able to do one AH if he chose to.