we need to know your location approximately. I wasn't aware there were any full time Chinese language stations in the UK and it would be interesting to find out where these are available. What I would really recommend is that you obtain an internet radio if she has internet access. You won't be bound by location or even nation with one of those!
It may not be an option you are considering but an internet radio will allow your mum-in-law to listen to South East Asian/Chinese radio stations from the other side of the world. Worth a little research at least. And think of the kudos you'll get! Mrs Yaffle enjoys Singaporean/Taiwanese radio stations as she has migrated here from Singapore. One to consider for CNY. Obviously a wireless broadband connection is required too. I've got a Roberts Stream 202 radio and it's doing the business for me. You can get cheaper wireless wirelesses though!