What a lovely generous thought. I think that would be a ********** if she could get somebody to take care of the children for her. Are they very young and would childminding be a problem for her.?
Probably you don't own your own company and have it within your power to dictate her holiday arrangements, otherwise an extra week's paid holiday would perhaps be a special luxury for her, if you could manage without her for that length of time.
For a less expensive present, perhaps for another occasion as she sounds a very practical person who is obviously keen on allotments and growing her own vegetables, perhaps, a year's subscription to the magazine Kitchen Garden, might be up her street. (via www.KitchenGarden.co.uk). Or something useful related to her hobby such as a fruit and vegetable drying dehydrator (available via the internet) so she can preserve all the fruit and vegetables she grows.