What kind of "stuff" are you talking about? Any valuables? Anything you wouldn't want to bear the cost of replacing if she should ever return looking for it?
There is nothing to stop you from getting rid of it- but you could later be held responsible for the property.
If you have means of contacting the ex-roommate try and get that person to come get the property. You can also put the property in a storage unit so it is out of your way.
Whatever you do with it, photograph it and inventory it so there is little to dispute over the contents if she later returns. Also contact her or make a public notice so that she has opportunity to get it before you do anything.
No, you don't have to keep it forever.
If it were me, after 9 months I would be looking to store it somewhere out of my way that isn't going to cost me anything. If I didn't have anywhere to put it, and if there were no valuables, I would simply toss it- but i would be responsible for the value of that property IF she came back for it AND IF she decided to take me to court over it.