Not to toot the custom route too loudly, but there is a real reason CX bikes do not come in small sizes. Standover is one issue, but the greater issue is your top tube length or reach to the handlebar. Because CX bikes have bigger tires, and all CX stock bikes come with 700c wheels, you have a larger diameter wheel to contend with when designing the frame. This means, unless you actually lengthen the top tube compared to the same size road frame, you will have toe overlap issues on any short-top tubed CX bike utilizing 700c wheels. Because most manufacturers don't want or legally cannot have that, they have overly long top tube lengths for their smaller frames. There is really no way around it. I hope that makes sense.
When I design CX bikes for smaller women, I go with 26" wheels. It is the right thing to do to make the bike fit without weird geometry compromises, or having to use a 6cm stem on a 52cm top tube (which creates its own handling issues). You know what I am talking about! The nice thing is you can get very light, road-like 26" wheels these days and CX race-legal 26" tires (in 1.35" width). There is really no compromise going this route, except of course the extra expense to go custom. Anyway, I do a lot of these, and hopefully some of the bigger manufacturers will eventually see the light for those not able to afford the custom route.