Net pay on £25k is around £1600 a month, assuming a 10% pension contribution.
If that nurse was living in my area, they could easily be paying £1,000 a month in rent, they'd need to run a car so they could get to/from work during late/early shifts (average cost £200 a month), and they'd be paying at least £100 month in council tax.
After bills, that doesn't leave a lot to live on, and I can easily see how an unexpected expense, like a broken washing machine or car repair, can leave them needing to use a food bank.
If they're earning a little more and have to start paying back student loans, they could easily be struggling.
But it's the rent that's a killer, and that varies widely between regions. And it's why a nurse in Brighton will be worse off than a nurse in Blackpool, despite earning the same.