Oh. NOT have the power to read minds like River.

Okay then! That works.

...Weaknesses? Otherwise this character is sounding a little too over-powered.

If a character has NO drawbacks, and can do ANYTHING, and no other character can compete with them, the audience rather quickly becomes bored. Not only does the audience not relate to perfection, but such characters rarely have any interesting internal conflicts, personality traits, or indeed CHARACTERIZATION. This makes them less so much an interesting character or even a character in general, and more of a list of powers and abilities. A list doesn't have an interesting story. It's a list.

River's insanity is a direct limitation on her incredible abilities, which adds some tension to the moments where she's trying to warn people about something but can't get it out. Will they believe her? Will they understand her (and interpret her correctly)? She can be triggered, which makes her uncontrollable by conventional means, and she might do things that draw attention to her or that she might otherwise regret. It's difficult to tell her insanity from her behaviour when triggered, which could cause some conflict/mistrust/concern with the rest of the crew. She has a sleep phrase so she can be stopped when triggered (and possibly when she's not, also a potential problem).

Her problems are what make River an interesting character and valuable addition to the exciting nature of the story. River without her problems is an over-powered psychic assassin who would make all the other characters superfluous... Which is a disservice to people who like the other characters.