I have a suggestion that won't be easy for you to do because I can tell your just like me! She needs to be confined in a carrier or crate with her litterbox and food and water. I know, I know!!! I hate to cage them up too!! The reason Tito came to you fully trained is because he was kept in a cage at the shelter. I know you don't want to do it and she will scream and drive you crazy but maybe if you just do it at night she will get the hang of it. It is really hard to make them stop once they start going outside the box. She is very young and tiny but if she started off ok and is now straying from the box, a pattern will develop. If you can manage it I would try if for a few weeks and see if it helps.
Another thing you might take into consideration is that once you take her home and she starts using the potty outside the box then Tito may feel the need to try that too! You know how they are about scents.
She is so daggone cute that it has got to be hard to anything but love and kiss her to pieces!!!