Giving in to her and rocking her to sleep is not fixing the situation.... It's just prolonging it. Put her in the playpen and let her cry it out. Hopefully you have a separate room for her and put on music or a fan or the tv to drown her out .... Ask mom for her pillowcase so the child can smell her and stop rocking her .
Do the parents carry her around all day? Did they not do any prep to get her ready for group care ... I would have a tough time with excessive crying .... Know your limit and dont forget you have a responsibility to the other children in your care as well.