She is not going to go up to 1500m - ever. Coe started off as a 1500/3k guy in HS, who moved down to 800m in College, so his experience/development has nothing to do with Femke.
Agree somewhat with Fisky - Tempo runs or even long runs (1hr+) are really not necessary (hasn't helped Mu). More VO2max work would help, but needs to be careful to not overdo threshold work (if any), as she wants to maintain her speed (400 in 49). If she wants to save her legs, some volume XT might be better than just longer runs. More volume of shorter VO2max reps may be better than longer reps (like the Billat reps, which are VO2max, not LT.)
49.0sec + 7.5sec = 56.5sec x 2 = 1.53. Is that too low a differential for her?
Keely at 51.6 slows 5.7sec to 57.3 for 1.54.6. Werro slows 6.9sec (hasn't run a 1500) from 51.0 to 57.9 for 1.55.9. Werro has also run 2.34.8 for 1km. Keely hasn't run a 1500m this decade. Kratochvilova ran 47.99 to run 1.53.28 (56.64) so a differential of 8.65 at an even later point in her career.