First, although the Twins roster has issues, the second base position is not one of them.
Second, Lee is definitely not ready. Last year, his only season at the AAA level, his batting stats were below average across the board and he had a wRC+ of 78 in 38 games.
Activating Lee is a break-glass-in-case-of-emergency solution, and as other posters have stated, he won’t be activated unless the Twins suffer significant injuries to their infield.