[Chris Saper]

Hi Mary,

Bright light on very fair skin leaves you very little wiggle room to show a highlight. Switch temperatures. For example, if your subject is in bright direct sunlight, use the very lightest blue, violet or perhaps cool green to indicated the highlight. If your subject is under bright cool light, use a warm note for the highlight.

Overall, if you're working from a photo, remember that the lightest several values are likely to be clumped into one bleached out area, so you need to decrease the key of the painting accordingly, sneaking up on the lights. You also need to make the value transitions into light in small increments or you will get the chalky appearance you're talking about.

And, BTW, congratulations!