They're not looking into the Capital Gains Tax issue so much though, as I understand it they're now looking into whether she was registered to vote at the wrong address, based on a complaint made by Tory party deputy chairman and Bury North MP James Daly.
Once again, it doesn't seem clear to me that there really is an offence here. According to the Electoral Commission website:
Now, the house she was registered at was the only house she owned and she has pointed out that she still spent time there (how much is a matter of debate, apparently) still paid all the bills for that house etc.
Daly says he has info from former neighbours of hers who will dispute her claim to have not been living full time with her husband before she sold her house but I have to wonder about how reliable that info is.
Even if some of her former neighbours are saying that (and we only have Daly's word for it so far) unless they kept a log of the exact times and dates that she entered and left the property then it seems to me their impressions of where she spent most of her time might be open to question anyway.