I would say if you want her because you feel bad for her then it's the wrong reason. If you want her because this is the kind of second dog you were hoping to introduce at some point anyway, then go for a trial.
My concerns would be;
1. The safety of your cats.
2. The length of the trial, in my experience there is usually a honeymoon period of a couple of weeks before you see the true colours of the trial dog. Would you get too attached in that time, and would you be able to fairly assess whether it's going to work?
3. The safety of your cats.
Let us know what you decide