Typically it is understood between both people involved in the ONS that it's going to be just that, a ONS. However, if you feel like you want to spend more time with her, call her and set something up. She may feel the same way as you, and is going through the same dilemma that you are.
Whether or not you want to start a relationship with a ONS is up to you. Most guys are too insecure about that and can't trust a woman who slept with them on the first night. They assume that if the woman slept with them, that they *must* be easy and a wh0re. Doesn't really say much for their own self-esteem but that's another issue. You'll have to date her for a little while, and get to know her. See if she's a person that you think you'll be able to trust. There are pleanty of women who choose to have a ONS because they want it, not because they can't control it. And if you can learn to trust that they will be committed to you then I say go for it.