Hello and thank you for posting.

I'm sorry you are going through this with your mum.

It is not unusual for patients to feel an initial increase in pain after radiotherapy, it is often called a radiotherapy flare. Please do talk to one of your mum's team about her pain so that they can organise some appropriate pain killers. In the meantime do give her some over the counter medication to relieve the discomfort until it is all sorted. 

Here is information on radiotherapy for bones which if you scroll down to the external beam section you will see this pain flare discussed as a side effect.

Take care and hope Mum gets more comfortable soon,

Sarah.