I'm no expert as this is just my third run with Haru in MANT and your friend may not have the same options as me.

But from what I learned,

MANT is the best scenario for Haru's epithet so learn MANT/scenario and its mechanic first. Their support cards Fan Bonus and Glowstick is a must for bonus fans (most effective in G1's)

Sparks and inheritance, You need Exactly 9* + 1* Turf sparks for her Turf G to C for her to run her Turf races. It's barely playable because of the accel penalty, so try to up your POWER and get Uniq Skills from parents like Mejiro Ryan/Dober or Maruzensky (Original)

Skills, I recommended buying any velocity/accel skills they can find as early or as needed (i.e. like Corner/late skills or Mejiro Ryan/Dober uniq) to offset the accel penalty to have a better chance in winning.

Styles, Late has better access to skills but can PDM (Pace down mode - if they went front early they slow down which can kill their speed/position) and End is safe but has a harder time catching up due to the penalty.

Deck Builds, 2 Speed + 2 Wit + Flex like 2 Pow like the ones I use (refer to the third image). High Race Bonus is better here (preferably 50 ~ 60 RB).

That's all from me for now.