In general terms I agree with the last post 100%, but maybe not in this case. The female in question is 3 years old. She is clearly mature yet weighs only 40 grams. If she is healthy and her tail is fat then 40 grams may be just fine. Some geckos are smaller than others! I have several females that never reach 50 grams even in the off season yet breed with no problems.
In this case, use your best judgement; does she appear healthy? Does she have enough fat reserves to keep her strong through the laying season? If so, then go for it.

John Yezbak
North Coast Geckos