How many days does it take to complete a complex LEGO toy?

I'm planning to give my friend a super cool and complicated LEGO set as a birthday gift 😄. She really loves building things, but... I'm a little worried. I don't want the set to be too big or too complicated, so that it takes her a long time to build and she ends up finding it too difficult.

For those of you who’ve tackled the big LEGO sets, how long does it usually take to complete one? A few days? Weeks? I just want to make sure it’s a fun gift that they can enjoy without feeling pressured to spend too much time on it.