that depends .
Does her book really sell?
Is her book geared to a target audience ? Meaning.. the people who buy it MUST like that kind of writting style..
Is she catering to the needs of that target audience?
Or is she trying to cater to a diffrent audience, and just completely missing the mark?
If she is writting specifically for ( example) 12 year old kids. And it READS like a 12 year old's book.. then right on for her!!
If she is trying to cater to 30 year old males.. but writes like a 12 year olds teenage drama.. then i would take that stand point.
i would say, " I know you are trying to reach blah blah market. Blah blah market buys ( list some titles) kinds of books like crazy. Have you thought about going that direction? "
and completely stay away from her 'ability' because her ability has to appeal to someone, or it would sell.
No matter how bad it really is..