...If Pippa really, *really* wants to save money, then she should focus on the limited packages that bundle discounted jewels, using the monthly pass + completing content efficiently each day, as well as learning to stop pulling once she hits a single copy of the unit she wants.
I don't believe she has the self-discipline to actually do this effectively, so it might take her a month or two of overspending to realize that it's a problem! Maybe!
EDIT: Non-discounted, assume $100 spent on the currency = 50 pulls. 200 pulls for a unit = $400 maximum, non-discounted. Unless she is flush with cash, she should take every possible bundle/discount that she is (financially) able to!