There are several rules:

short ~ one month playthrough must be enough
nice graphic, preferably 3D third person and colorful, but open to suggestion outside this requirement
fantasy - a must!!!!!!!!!
female protagonist preferable, costumization is OK,, if you can't think of a any game, then male protagonist (or any animal/human/undead) is fine
rpg elements - don't care if it's jrpg, any rpg or minimalistic rpg game will do
gameplay is almost irrelevant, as long there is gameplay

gog and steam are fine by me.

Really dislike graphic style, combat/gameplay seems like something I would personally dislike more than graphics.

How about Wonder Boy: The Dragon's Trap?
Here's how it fits your requirements:
short: The game is only a few hours long, so it qualifies.
graphics: The graphics (assuming you're playing with modern rather than classic graphics) are hand-drawn, and are quite colorful. The game is a side scroller.
fantasy: Yes. The bosses in this game are dragons, for example.
female protagonist: Yes, if you choose to play the girl. Note, however, that you spend basically the entire game cursed into various animal forms, with different abilities.
rpg elements: There are weapon, armor, and shield upgrades, and you can equip them through a menu screen (a few even have special effects). There's also a currency. No levels and experience points, however.
gameplay: Game is a side scroller.

Incidentally, if you are open to other Sega Master System games (that don't have GOG versions), there's also the original Phantasy Star.

Ah, Kingmaker! I played that with pen and paper.

About game suggestions... have you tried Shadowrun Dragonfall/Hong Kong?
It is not your typical fantasy, but for the same reason it is imo even more interesting. The visual is top down with 3D characters.
You can build the protagonist however you like.

Also, The Banner Saga is an interestig take on Nordic mythology. The protagonists are both men and women.

Checking:
Wonder Boy
maybe I got both later Shadowrun games at reddit giveaway, otherwise, they will be on my waitlist.

I have some sort of déjà-vu feeling with these posts...

Some other suggestions:

Hand of Fate 2
Exanima

I know I shouldn't mention this one here on GOG, but, have you tried <whispers> Armello?

Hands of Fate 2 is on my radar, but Armello's Vac possibilities is off putting.

I will recommend the following games provided your requirements of female protagonist, short, fantasy, nice graphic.

1. Female Protagonist, nice graphic, fantasy, short, rpg

2. Female protagonist, nice graphic, short, not fantasy but based on harsh reality/bad experiences that females go through in their lives

3. Female protagonist, fantasy, nice graphic, short