Ask the expert: Return from maternity leave

I have a bit of an unusual situation. We have a lady who wishes to return to work at the end of her paid period of maternity leave (nine months). She has given us less than the required eight weeks' notice, but when informed of this she claimed she did not know. However, we thought it may suit us if agreement could be reached and she was informed of this. Before maternity leave, she worked three days per week (the result of a previous return to work agreement). We actually wanted her to return to these three days, although we were willing to be flexible over which days as long it fitted with business needs. But she is asking if she can return for two days only, and not on days that we need her most. I would like to reach a compromise, but due to the needs of the business I am running out of negotiation room. Any advice or thoughts?