The mind has room for virtually infinite languages, scientifically speaking. Duolingo is decent for learning new words and phrases, but it isn't great for speaking practice. If you don't mind me saying so, Pimsleur language programs is far better for a focus on listening and speaking.

It's so fun that your daughter is learning Korean! I taught in Korea for about 3.5 years and learned so much! If she wants some tips for learning Korean, my DMs are open. Recently I vibe coded a Duolingo like game but with lyrics from a Korean song, so as to improve my comprehensible input specifically. It's super fun!