Master has thought Acceleration and multi-thought skills, meaning he can act first.
With that he will usually first appraise the opponent, which gives him information about stats and the the opponents abilities and what the abilities do.
Assuming he evaluates the Overlord as a very dangerous individual based on that, I can see him instantly stealing his most dangerous ability with Skill Taker SP.
Fran would in the meantime open by launching a spell at the opponent. Lightning or Fire spells would be a typical choice.
Regarding best traits: Fran is a masterful swordwoman, that can match opponents with much higher stats through pure skill.
Master has a spell that after its cast will resurrect Fran once. Additionally she has Sacrificial Bracelet, that prevents her death once, and a Skull Necklace that prevents her death once and restores half her HP and MP when doing so.
Aside from Skill Taker SP, Master's most dangerous skills are like his Space-Time & Dimension Magic Spells.
They include (selective) spatial intangibility, teleportation of himself and of others towards him, portals, a 5 second time stop, a spell that increases perception speed, a defensive spell that diverts attacks by twisting space and possibly BFR.
When in her awakened state Fran passively emits lightning, which conducts through metal, including armour and weapons. Like most lightning magic in the verse it likely also paralyses.
Fran has a Physical Nullification skill, that negates all physical attacks her at the cost of a proportional amount of mana. She also has a similar skill for lightning damage.
Should an opponent let go of a piece of equipment they will put it into their Dimensional Storage, a pocket dimension in which time is permanently stopped.
Fran has a skill that absorbs mana from the opponent and the opponents attacks on contact, as well as powerful magic resistant barriers.
With her optional equipment she also has Deathgaze, a sword that has a 3% chance of causing instant death upon causing a wound. The instant death works by stopping the targets heart.
Since Fran fights with Master and Urushi she basically always has numerical advantage. Urushi has a spell that makes the target blind and some mind manipulation spells to show illusions or make the target faint. He can also cause a poison mist to spread through the surroundings, which Fran is mostly immune to due to poison resistance. Urushi's usual fighting style is diving through shadows to land surprise attacks and restrain the opponent to give Fran the chance to land decisive hits.
Oh, and Fran of cause has enough Regenerationn to restores limbs and stuff.
No passive stuff aside from resistances, I think