The course could play entirely different tomorrow. There will be different tee boxes, different pin positions, different wind direction, dryer course, better/worse starting time, etc. Shooting a 71 on one day does not predict anything about what your score will be on Friday. One of my best friends shot 71 on day one of the U.S. open and shot 83 the next day to miss the cut by plenty.
That's an understatement. She handled the course very well today, missing only one fairway and only one or two greens. Brilliant play, actually. She obviously has given this course a lot of thought over the past few months, because her strategic play was perfect. If she repeats this performance tomorrow, I think she has a decent chance of making the cut. It'll be difficult, though.