skilful at singing

The sentence is fine but it has connotations that might not be intended.

Yes, someone can be a skillful singer in that they can hit all the notes and do everything with skill. But being a great singer probably requires more than just skill. There are a lot of intangibles like the emotion behind the singing, the connection with the audience etc that make someone transcend just being "skillful."

The statement "she is skillful at singing" seems to be begging for a qualifier.

She is skillful at singing, but .....

Thanks, Parados.

She could be very skilled at vocal technique, but lack the "soul" of a great singer.

Thanks, Noddy.