After you get a male, and it would have to be a male, females do not evolve into a Gallade.
Ralts will evolve into a Kirlia at level 20.
Kirlias are a branch evolution
Females can only evolve into Gardevoirs, and they do that at level 30
males can also evolve into gardevoirs too, but if you use a dawn stone on them,
they will evolve into a Gallade instead of a Gardevoir.
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Dawn stone evolves a male Kirlia into Gallade, and a female Snorunt into Frosslass.
You cannot get a Gallade on Pokemon Ruby. But you may get one in Pokemon Diamond or Pokemon Pearl. - Badminton
Gallade is both a fighting and psychic type Pokemon. Rock, ghost, dark, grass, and poison Pokemon can be weak against Gallade.
You have to learn it at the Platinum/HeartGold/SoulSilver Move Tutors.
Gallade is a evolved form of Kirlia (Evolved form of Ralts) but has to be a boy Kirlia. If it is, then you can evolve it with a Dawn Stone, and it will be a Gallade.