A lot depends on her mobility and lifestyle. Sorry, at that age, it is hard to guess what factors may affect the design and usage of the bag, so it is not in the way, as you requested!
A cross body bag style would keep it within reach and give some movement, yet still be able to get at it easy enough. Another possibility, might be to attach the bag to a waistband/belt. You could make the belt or use a real leather belt, with loops on the bag to slide the belt through.
Good idea for the pocket for a notepad and pencil. Maybe some other things .... kleenex? lip balm or lipstick? etc. So don't make the pockets too small! You might want to include velcro, zippers or buttons so nothing gets lots between uses. Can happen all too easily!
Good Luck!