I truly believe that the Le does not have enough evidence to charge her with murder or they would not be contacting Baez's office for Casey to talk about Caylee. Right now that is all they have is circumstantial evidence and the cannot tye Casey to Caylee yet.
Well, they could be contacting Baez to ensure that they have followed all protocol in following up with all possible leads including through Casey herself. If they didn't then the Defence could use this against them if trying to build a case that they did not do due diligence while investigating. (Hence, Baez's snide remark about how long it took...)