From my own experience & what other artists told me:
- Never say "you have talent". For many artists it translates into "you don't work hard - just use your talent every time".
- Your painting is very good: it looks almost like a photograph... (then whats a point of doing a painting???)
- Never give to an artist an artwork of another artist as a gift unless you are ABSOLUTELY sure he or she will like it. Just ask! We lot have normally very strong preferences in art!
PS. Personally I found patronizing words like "clever girl" be real killers...