I came across this sentence but don't know what it means about a girl's face/expression
My guess: "in her well-ordered face, is a dignified expression with a little bit of sharpness (?)"
Note this can be subjective to some extent.
凛【りん】とした gives an image of someone with a sharp, assertive, confident impression. This includes physical characteristics, so political correctness (or whatever) aside, it is not commonly used for fat people. As such, 尖【とが】った probably means here something close to skinny or bony (which may not have positive connotations in English).
For example, Audrey Hepburn in the last press conference scene of Roman Holiday may well be described 凛【りん】とした. On the other hand, Marylin Monroe may be too glamorous to be called so. I'm not disparaging Marilyn Monroe, but her kind of beauty is not very consistent with 凛【りん】とした.
Another stereotypical element that comes to my mind is sharpness in eyes, again also in physical sense. So even Audrey Hepburn does not completely fit the description because her eyes are too large. Someone with thinner eyes that are slanted upwards (like stereotypical Chinese people) will fit the description better.