I got mine in a couple of weeks and hopefully she gets it pretty soon.

What address did she give, the school's international office address or her personal mailing address? She should be okay as long as it is the school's address. If that's her personal mailing address, make sure that she has a label with her name pasted inside the mail box, otherwise there are chances that it will be returned back.

You should have received the receipt by now. Mine came in about 7-8 business days after I mailed my documents to USCIS. I applied at the end of January though. And I received my OPT card near the end of March. It's taking longer probalby because they are getting too many applications these days. You should get the receipt pretty soon. Contacting USCIS may not be a good idea as they get ticked off for no reason (One of the staffs at my school's international services told me that USCIS can deny your application for minor reasons like going outside the area designated to write/sign.)
I'd say, there's no reason to be alarmed for a few more days; you'll probably get the receipt by next week. Good luck.