This will not end well. What you have is a classic case of 'The blind leading the blind'. You're absolutely right, everyone starts somewhere, but if the child's parents have preconceived notions about the result of this shoot, then I would stay away from it. If, on the other hand, they understand that you're new as well, and that this will most likely be a 'throw-away' session, then by all means go for it.
As for resources, first and foremost, what type of modelling? Is she serious about modelling, or is it just a bit of fun? Does she meet the basic criteria for her intended genre of modelling? There are actually some good resources on MM, but you have to be a member to access them. There are a million tutorials on YouTube, but for my money, the best information is almost ANYTHING from
Lindsay Adler.
Start by learning the basics of what makes up a basic portfolio (comp card/Z sheet, two heads, two full bodies, 'range of talent' shots) and what you need to create those images. Analyze the model and plan EACH shot, but DO NOT plan to do this all at once. If you're looking to produce a whole portfolio for her (10 images + 'Z') allow at least TWO sessions. Make sure you have the lighting; three lights are the MINIMUM, and four - five are better. Talk to her (and the parents about where she's going to sign, and review the images from that agency. Understand what agency reps are looking for, and spend time working out how YOU will create them.
Good luck!