Well, you're "allowed" to miss up to 6 weeks per year for holidays/illness and in theory you could use them for days when you didn't feel like it or whatever (after 6 weeks are used up you have to pay for missed weeks). Of course, a lot of people who miss a week or two come back and find they've gained, or hardly lost in that time, the weekly meeting is usually a good plan for keeping oneself on track/focussed. If she's worried that she's not done that well this week, going to class is probably the best thing she could do as that way she will know the damage (or maybe even be pleasantly surprised) and get lots of advice for getting whatever she may have gained back off, which will hopefully help motivate her.