I'm not 'punishing' her since I'm not sacking her or suggesting she should be sacked. I'm pointing out that it would be good politics that while she is under investigation that she isn't minister for corruption. If you are holding yourself out as better than the previous lot, then what things look like are important
Of course it is if she has to step down - if that happens, she would have had a ministerial job, and then she doesn't. In what way is that not 'punishing her'.
And what ever happened to innocent until proven guilty - and in this case there aren't actually any allegations. If this happened in any other employment context I cannot see why she would be suspended from her role while the investigation, let alone be expected to resign or be sacked.
The 'previous lot' are hypocritical in the extreme - they had two PMs who received criminal convictions for crimes they committed as part of their jobs - and they were the ones who put in place the laws which they themselves received criminal convictions for. In one case the PM eventually resigned, but not specifically for this, in the other the person was selected PM despite that criminal conviction for what they did at work.