Yes, Garchomp can be female.
Garchomp is a dual-type Dragon/Ground Pokémon that can be either male or female. Like most Pokémon, the gender of a Garchomp is determined randomly when it is encountered in the wild. This means there is an equal chance of finding a male or female Garchomp.
However, there are some exceptions. For example, in the Pokémon games, some Pokémon are always male or always female, regardless of their species. Garchomp is not one of these Pokémon. Therefore, you can encounter a female Garchomp in the wild, just like you can encounter a male Garchomp.
In the anime, Garchomp has been shown to be both male and female. For example, Ash's Garchomp is male, while Cynthia's Garchomp is female.
Ultimately, the gender of your Garchomp is up to you. Whether you choose a male or female Garchomp, you can be sure that it will be a powerful and loyal companion.