The clock for the prosecution starts ticking away as soon as they arrest and charge an individual, therefore they want to get as air tight of a case as possible before going forward with that. In this case, there was a TON of evidence they had to wait for via warrants - like the GPS evidence from phones and cars, Google history, etc. Each of those things is an individual warrant that has to be served to each company, then each company has to honor it by compiling the information requested and sending it back. All of those steps take time. Then, once all of the evidence is compiled, they have to tidy it up into a neat package to present in the AA for a judge to sign off on. On top of all of that waiting, they were watching her and gathering more evidence from her behavior to use as well. All of the waiting can be frustrating, but they do it in order to make sure a case isn't mishandled and that they can secure a conviction down the road.