I'd say VDusen04 nailed a lot. One thing that is important (that you haven't mentioned) is the level of the competition. Either way, your main focus should be on defense. Offensive skills take time and willingness to learn but anyone can play defense if they want to. You just need to access your girls' athletic ability and build a defensive strategy based on what you have. Shooting from the unknown, I'd say your base set should be a packed in 2-3 zone. I agree with VDusen04 that fundamental man to man D is the way to teach, but I think we can assume you aren't preparing any of these girls for play in college, and you will probably need the extra time to work on other things.
I think the mistake a lot of coaches make is to assume that you just throw kids in a zone and call it a day. You should TEACH the zone. A 2-3 is fairly simple to grasp but there are holes and you should focus on how to cover them. You also should drill rebounding when in a zone because it's harder than when you can just find YOUR man and box them out. But a packed in 2-3 forces outside shooting and clock milking ball movement... both good things for a team trying to play above their level.
Other than that, I'd say conditioning and fundamentals are huge. Your goals to focus on should be rebounding (don't give up offensive boards, try to get offensive boards for easier shots), limiting turnovers (dribbling to protect the ball, passing... both under pressure), and transition D (limit fast break points, force half court sets).
On offense, a simple motion should be fine. It doesn't sound like you'll have any stars you should build your offense around. You want something that you can teach quickly (like on D) so you can spend a lot of time focusing on fundamentals.
Could say plenty more and I'm sure VDusen04 could also. Let us know if you get the job and/or have any specific questions.
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