My youngest chi turned 1 year in November.
It's been my experience that they go through a phase aproximatly between 10 months and 1 year, like a teenager testing their boundries.
Stick with your potty training and if you catch her going where she's not suppose to tell her "NO" and take her where she's suppose to go. Be sure to clean it up well.
It seems like once they get past that 1 year old hump they do much better, as long as you have trained them correctly.
If you've had her spayed, I doubt that she's marking. It's pretty rare for females to do that after they've been spayed. I'd just reinforce her potty training.
I know it's frustrating, but remember as long as you've done well with her training she'll be back to normal soon