I was pretty happy to see a rustic magus included in the Magi of Hermes book. Rustic magi, along with folk witches, are probably my two favourite magus arch-types in Ars.
However, Julia's entry has me befuddled. From my understanding, based on this thread, the magus' casting total for non-formulaic effects needs to take into account the Spontaneous casting penality of divide by 5. Given that, I can't make the math work for Julia's magical cloth. At +45 years, Julia's MuIm=10+5+2=17, CrCo=9+8+2=19, CrIg=9+5+2=16, MuMe=10+7+2=19. Divide those by 5 and her casting total is not sufficient to enable her to create the magical cloth.
What you are missing is that I interpreted the rules in HoH:S without the need to divide by 5 (which in all fairness to me, is not specified in HoH:S). Bear in mind, Julia was written a long time ago, way before the discussion you linked, and before I knew Erik's intent with the rules. However, I would say that dividing by 2 rather than 5 puts Craft Magic more on par with using non-Hermetic Craft Magic; which uses the Craft Total - probably be much greater than the Casting Total of a non-fatiguing spont. Non-Hermetic magic shouldn't in general be stronger than Hermetic magic, even if it can do different things.
The differences between the totals you give and the levels achieved are accounted for by the die roll and the aura; since I assumed she was using fatiguing spontaneous magic. For example, she might fail the MuMe15 effects, since she has a Casting Score of 19, +6 for an average die roll, and +3 for a typical aura; resulting in an average Casting Total of 14 after division by 2. She can also get a bonus to her Casting Score up to her Craft: Linen or Craft: Wool (as appropriate) with shape and material bonuses, which is sufficient to achieve more reliable successes.