Good advise here Mom! Send flowers, a note or a little gift. Tell her how much you love her. Also, tell her to keep her head in the books, because it is very easy (even for the best of students) to get behind with all the recruitment week events. Maybe suggest she find a pledge sister to study with in the library or something like that.
Also encourage her to make the most of her new member period by getting to know all the other new members as well as the actives, attending meeting, philanthropies or any other events that they are having. Some chapters have weekly study hours (where members meet in a certain location on campus and study together) or meet on a certain day in the cafeteria for lunch, that sort of thing. By throwing herself into Pi Phi, she will start to feel the wonderful sisterhood and sense of belonging that made her pledge in the first place.
To me there is nothing worse than a new member who sort of "sits on the outside" and does not get fully involved with chapter life. As an adviser, I have seen it a few times and it really breaks my heart.
No one in the chapter knows if they were her #1 or #2 or #1,000,000 choice (unless she is foolish enough to say something, which she shouldn't). And you will know, if you read much here on GC, that many, MANY women pledge their #2 or #3 choice only to turn around and say "I don't know how that happened, but I AM SO GLAD IT DID. THIS IS MY HOME. It happened for a reason".
As for you, try not to worry (yeah, right) and just be the wonderful, supportive Mom you are! You are lucky Parents weekend is so soon. At my school it is in the spring, so the parents have to wait!
Please post how your daughter is doing! Pi Phi is a wonderful sorority and she is very lucky to have found her home there!