The faster and younger she gets to a major airline the better her career will be. She could be in the job market by 22-23. It takes effort, drive, and money.
She can have her CFI before she starts college. AP courses and community college means she could be entering her third year of college by the time she is 19-20. Get a two year degree and continue towards her four yr degree (currently a 'must' for the big airlines). As soon as she gets 1500 hrs or her two year degree, or earlier, start flying full time and transition to part time, but year round, four year degree program. She could be 23 yrs old (+/-), with a four year degree and 2,500 (+/-) hrs total time.
Similar to what I did and I'm fairly lazy. Graduated at 23 y 9 months with 3 yrs 2 months, and four jobs, worth of work experience.