How to build neutral LF Robin?

You can also put flier support on her C slot. With this build she tanks and kills even B!Lyn , but you need an alliebwith fortify fliers for max effectiveness

I want to know the IVs and start my recommends there but...

(if +spd)then go with desperation for be skill and change a skill with an offensive skill if you want her to kill units more but she'll be more easily killed.
(if +atk) same with first one
(If +def or +res) give her Qr and distant def seal so she'll have a really easy time tanking range units or go with close def for melee units.(but she's not the tankiest so don't expect her tanking hits easily especially against Raven tomes and Falchions.)

It's easier to build her as an enemy phase because of her native dragon skin. Just put on QR on her B-slot with Dist Def seal or Renewal with QR seal and then goad flier for C-slot so she can support your more offensive fliers. They're very good high SP skills that can help in arena scores too. Res smoke doesn't really help flier teams much because tome fliers are rare. In any case, they're better off getting buffs with bladetomes rather than lowering the resistance of a target unit.

If you think she can double often (meaning she doesn't overkill on her first retaliation), keep Bonfire. Otherwise use Ignis so she has something to nuke with on the next player phase.