Most hearing aid suppliers will refund most of the money within the first month. They usually charge a fee of about �150 to cover their costs. Many people do find it difficult in the first few weeks, and she should contact the hearing aid audiologist to see if adjustments are required. There is a legal requirement for your mother in law to be contacted to see how she is getting on, and this must be done within 6 weeks of the fitting date.
You do not say why she does not get on with her aids - if they are uncomfortable they can be remade. If she does not like the sound then they can be adjusted. Your mother in law will need lots of help and encouragement in the early stages - so why not arrange to be there for the follow up call.