What is problem with my friend who can not sign freely on bank checks but signs freely on waste papers?

whenever she tries to put her signature on bank checks, her hands shake and she had to tear 2 or 3 checks so that her signature tallies with the signature available in bank records. but she signs freely and without any problem, on waste papers and papers other than bank checks and her hands don't shake and perfectly tallies with the signature in bank records. what is her problem? how to solve it?