Preganancy Placenta

Patient: My Wife is Twenty weeks Pregnanat. Just two days back she ahs done some hard works cleaning floor and taking little bit weights. When we scanned the scanning reports shows below,placenta Posterior Grade One lower end is just touching int OSDoctor suggest to take rest. This is Second delivery. Is there any problems. How long she has to take rest. Any precaution to be taken. Please help me Doctor