Unless she is naturally frugal, I suspect saving 80% is an unreasonable expectation.
I have 1 young adult at home, working more or less full-time and doing uni part-time.
He is naturally very spendy and went overboard a bit but first year out from school there were significant expenses that were legit:
- bought a car, essential for his job. Secondhand. 14 years old, Cheap. Interest free loan from me which he paid back in under a year.
- ongoing expenses in running the car, needed new tyres etc etc
- business attire, suit/shirts/ties/shoes - then dry cleaning costs ongoing
- phone up grade and laptop ( went overboard here IMO, but IT is his thing and he makes good use of them) - then more expensive phone plan ongoing
- uni books and other uni costs etc
He paid his mum some board, but by the time he paid for all of the above I don't think much was left over. Socialising is also an important part of a budget in this age group.
I showed him figures how early investment into a retirement account for a few years will be more effective than leaving it 5 or 10 years to start and he took this on board.
This year he is more set up and his costs are lower, and he has got bit more interested in saving and investing - he mentioned he was saving nearly 50%, which frankly I am overjoyed about.
I haven't promoted an expectation of 80% savings because I haven't personally achieved and modelled that for my kids. I encourage them "to save 50% and after about 20 years, they will be able to retire, or do whatever work they want. " I figure once they "get it", if they want to go harder they will.
I think be around, build the relationship, talk about finances, help her with her budget and show her there is an alternative to YOLO. By all means mention some people save 80%, but unless she is naturally frugal I think this will seem so extreme as to be off putting.