On her main mix up b14, the oh into low, she is unsafe. But of course they will likely cancel into military stance in covert ops, her most popular and easy to use variation, which if blocked correctly is also unsafe. She has the option to 1. overhead cartwheel 2. low flip kick thing 3. cmd grab. The low option only leads to combo in the corner, the command grab option you must watch for/try to read. Cartwheel is the most common because it leads to the most damage and most players tend to favor ducking. All her specials are unsafe regardless if EX'd or not as is the dive kick except for at rather specific distances, but you still get pressure afterwards. The low starter into two mid hits is not unsafe if I recall, but you do get pressure. Again though you will be dealing with the military stance mix up.
There is of course more to the char than this, but that's the basics and what I believe gives people trouble. I suggest that you zone/space her as much as possible. Be sure to look out for the evasion of your spacing into dive kicks, it's most Sonya's bread and butter. So watch out and blow it up if you can. It recovers really fast on whiff, but is blown up on block in most cases.
Her mix ups are really good IMO, but that's a basic run down. It's not easy to deal with her when she gets on you.