Standover height is only one parameter in a suitable touring bike fit, and the overall fit must be right if the bike is going to be enjoyable to ride. In any case, for a touring bike, you don't need that much and a propely fitting frame will inevitably have sufficient to allow Mrs RT to stand up on flat feet in front of the saddle.
IME (or rather that of Mrs
the most important parameter in fitting a woman's frame is reach to the bars - sure, this can be tweaked with different sized stems but it needs to be nearly right.
From the measurements you've given I'd suggest visiting a bike shop and trying a 54cm centre to centre frame, or consider a 56 with a reasonably short top tube. A 56cm man's frame is likely to give too long a stretch to the bars. The problem is that everyone has different proportions and the only way to find out is to try.
If the bike you have an eye on is stocked by
Evans, they have an online sizing wizard that might help.