16 months is a difficult age to stop breast-feeding as it is very difficult to explain to the baby at this age.
You will have have to stop it at one go. Explain to her that it is no more.
She will cry, get her favourite snacks, buy her small gifts, encourage her. For a few days try to keep your baby with you away from mother. When ever she asks for it, refuse it. Do not force her feeders or milk. Make dairy desserts for him. She will take around seven days to settle.
Nights will be tough. At night when ever she gets up for milk offer her juice/water.