Quite honestly, the amount of money involved probably doesn't matter that much to Michelle Mone. Her husband is a billionaire and I'm sure they won't be poor (although, of course, the money could buy an awful lot of school meals or do some good).
The point is that this woman has an important constitutional role and all the power and networks which go with that. Hopefully, the investigation will be transparent. If there is actual fraud, she needs to be prosecuted. If the investigation shows any other kind of "dodgy" dealings (even if not quite illegal), people will know what they're dealing with. It would be a first step towards restoring some kind of trust in the people who are governing us.