The area of expenses can be quite difficult to get a handle on, especially if she is self-employed as a Sole Trader as opposed to an Owner/Director of her own Ltd. Co.
Some people will tell you that you can't claim for lunch regardless, because everyone has to eat. Some people will quote the 'subsistence' rule for Ltd Co. employees and use that as a guide.
However, from my understanding lunches can not be claimed. The general rule of thumb is anything that is genuinely used for business purposes can be claimed. For example, a percentage of home heating/electricity (if working from home), a percentage of all car expenses (if private car is used for travel to clients premises to work). A quick chat with an accountant will give you an idea of what these percentages can be, based on your level of use of each.
Other general expenses like equipment, stationery, advertising etc are all acceptable.