there’s some good advice on here and some that probably doesn’t apply. i would suggest contacting an advice agency rather than jobcentreplus or the pension service as in my experience they don’t give the best advice.
there’s cab’s in most areas (quality of advice at these is highly variable) and many councils run their own service too
i’d need to check but i don’t think she’ll qualify for a bereavement payment as it sounds like she’s over 60
sorry for the loss, and i’d guess your mum might not want to think about money etc – she should have 3 months to start making claims for anything she is entitled (probably pension credit and council tax benefit)