You don't need to rely on equipment to get great shots. Your Panasonic 20 f/1.7 and 14 will do just great (though honestly for preps I think the 20 will more than get the job done!). Pump it up to ISO 800 or higher if you need. Bring along a flash and toss it on - you can easily turn it on or off, but the good thing is, the option is there if you need it.
I mount my Nikon flashes to my GF1 all the time and use manual mode (it'll be easy too - set it to 50mm and adjust intensity yourself). Be creative with bounce: off ceilings, walls, etc... I am sure your sister will be happy with your results.
You have a couple of photos that are great... you must be very good at photoshop!