Mum has Breast Cancer and just had radiotherapy - should she be going into shops and cafes?

Hi, thank you for letting me join your group. My Mum was diagnosed with Stage 2 Breast Cancer during lockdown. She was lucky and was treated quickly and had a lumpectomy and decided against Chemo as she is 75 but had radiotherapy and finished it last week. I live 200 miles away and am going to see her on Sunday with my children for the first time. She had a shielding letter in June and she says she is self isolating but she is going out with my stepfather and eating out at cafes and has been to the supermarket and other shops. I don't think she should be doing this as surely her immune system is too low. She says she is self isolating but I didn't think you were meant to go to indoor shops and were only meant to go out for exercise where there were no people to come into contact with. My step father doesn't want to stay in the house and wants her to go out with him. I don't want to upset her by keep mentioning it each time she says they have been out but I am so worried that she is putting herself in danger and I don't know what to do when we go and see her. Am I right that she shouldn't be going out to shops or cafes when she has just had radiotherapy? And that when we see her we need to meet her outside the house in the fresh air and not inside a cafe? I would appreciate any advice anyone has.