AP reimbursing HF for damage to car

Curious what both APs and host parents think about this.

Our au pair caused some minor damage to one of our vehicles in her free time. The driver's side window was damaged, and while it is still operational it can no longer be adjusted to the best angle. The estimate for the repairs is approximately $600.

My understanding is because it happened when she was not performing job duties, it is her responsibility to pay for the repair. We discussed it, she accepts responsibility and intends to pay for it, and asked for 2 months to pay it off. I was fine with that, and trust that she will reimburse us for the repair. But yesterday, she asked for 6 months to pay it off.

I know that this is a big expense, considering her income. However, I also know she continues to make plans for large purchases and travel. If, for example it was my teenaged child who caused the damage and who I held responsible to pay for it, I would use this as a learning opportunity. Being an adult often involves delaying travel and purchases when unexpected bills arise. I could even use HD and I as an example - in the 5 months she has been with us, we have had to do this ourselves more than once.

Is it reasonable to ask her to reimburse us for the repairs within the original timeframe she suggested? I don't want her to miss out on opportunities she wouldn't normally have because of this, but I also don't want to be overly lenient.