Hi,
This is an awesome project! I hope your daughter has a lot of fun with this one.
So, first, did you consider how you are going to maintain a 130F temperature? What do you plan to do if the temperature inside the heap starts to get over 130F? This could get tricky - and Sunchips says it should take 12-16 weeks to decompose. They didn't say why there would be so much variation.
http://www.sunchips.com/resources/pdf/S ... Scenes.pdf
They did test it two different ways. They got fastest results (13 weeks, seemingly consistantly) when they added other compostable materials and did not control the temperature (much like someone would do at home). Since you are trying to beat the 13 week mark, this is the approach I think you should be using. You can still use the heat lamp to get it going, or if you plan to store this thing in the garage in case it gets stinky.
The link I gave also gives some ideas for optimization. I think one of the most important is going to be getting the internal temperature to 130+ quickly and making sure it stays at least that high, have the best mix of other compostables and making sure it is a good enough size. Another idea is to use some compost material from an established compost - call some garden or landscapers for this! You may also be able to speed it up by increasing the surface area of the bag (cutting it into smaller pieces).
Even if the bag is not 100% composted at the end of the experiment, that may be ok! What is the question your daughter is trying to answer with her experiment? Maybe she could ask: "Will doing X speed up the decomposition of this bag"? Or maybe "Will cutting the bag up into smaller pieces speed decomposition?"