Sorry it’s late - I’ve been watching the crown and didn’t realise the time

never posted before just lurked previously but wanted some advice. I have a neighbour who has been mixing alot since the tier system/second lockdown she was ok in the first one - young woman with two small children and I do find her quite pleasant etc, she has a support bubble with her sister as she told me this herself and that is fair enough it’s allowed but this week she has had all different people round - not big parties/gatherings but just different households going round. Tonight I called at the local shop and she was there with a random bloke and two other people buying beer - obviously all going round to hers, my other neighbour messaged me on Facebook and said she had reported her on the online form you fill out (never reported anyone before so don’t know what that is) and that the police never came, she told me to do the same so it would be two of us but I couldn’t bring myself to do it - I’ve been bought up not to be a “grass” but it is wrong what she is doing. What do I do?? I’m shocked the police didn’t come to be honest thought they would be on it.