Ninetales is a Fire type with a weakness to Water, Rock, and Ground types. Her ability is Flash Fire, which makes her immune to Fire type attacks. When attacked with a Fire type attack, it increases her Special attack by a 1.5 multiplier. She also can have the Drought ability which makes it sunny on the battlefield for five turns.
She has a naturally high Special Attack and Speed so I will focus on those in making her moveset. The moveset I would recommend for her is:
The other two moves are up to you. Some safe moves are Dark Pulse (possibly flinching the opponent), Extrasensory (another chance at flinching), Hex (a fun ghost type move), or Hidden Power (depending on its type)
With her natural increase in speed, you can put them to sleep even before you get hit. This moveset is aimed more around Hex. It’s power is doubled if the opponent has a major status condition, which is where Inferno and Hypnosis come in, both causing one if they hit. Dream Eater is just nice while they are asleep, you can heal and deal damage.