Need advice on directors taking maternity leave in small business?

My husband and I.. and my sister run a plant garden centre. We are a smallish business and so all heavily involved. My sister had a baby three months ago and has worked right up until the birth of the baby but obviously in a plant nursery not up to 100% (she did brilliantly don't get me wrong) but now she has had 3 months where, although we insisted she took the time off, she has still been coming into work but doing 50% time of what we are doing and also no responsibility and coming and going as she needs to (again, understandably she has every right to as she should be on maternity leave). The problem is she is still taking the same wages and drawings and we can only claim back about a third off the government. This isn't a problem up until now but she has mentioned that SMP goes on for 39 weeks (goes down to �123 a week) and SML is 52 weeks. If it was an employee we would happily p on her �123 a week but she is taking her usual directors wage. Also more worryingly, we are wondering when we should expect her to take on her full duties and her full hours if she is taking her full pay. I don't begrudge her any time or money, we just want to plan the next year of our business and as the three of us are key in it, one person having no responsibility or set hours is proving difficult, especially at the pay they are commanding from our small business.... and yes, before any one says it, I too will be having babies in a few years but the third and equal partner in salary never will :-)