An employee of mine is asking for a raise. Like many employees, she thinks she is doing very well and should get a raise.

Her current compensation package is well in the market benchmark and also when compared to other employees in the company that have roughly the same title and experience.

The employee is good (not "excellent", but "good") and she shows motivation to the work.

I don't think she deserves it right now for various reasons (that I don't want to write about them here). So I'd like to turn her down about the raise, but I would also like to make sure her motivation will not be affected. I see a potential raise about half a year from now.

What should be the best approach for that?

I was thinking about telling her the points for improvements as I see them, but my concern is that she will lose her motivation.