Why don't you just see how it goes? There's no point worrying too much about it now. If she seems to struggle then you can try the 4 day week, but she might enjoy it and want to go every day! You can't really tell before she starts. By all means make plans, but don't set them in stone. Think of the 4-day week as a contingency plan for if she can't cope with a full week, and be prepared to be flexible. My son is still 3, he'll be 4 in August, and he's starting in Spetember too. I am way more worried about it than him, he can't wait!!