My cat has a brain tumor, help with some questions?

My poor baby Roxy has a brain tumor and she displays the majority of the symptoms. Lethargic movements, pressing head on items, meowing, confusion, pupil dilation, drinking a lot, loss of trained skills, etc. How will I know when she is in pain? My family can't do anything for her, so when she is in pain we are going to have to put her down, as depressing as that is. I do not want her to be in pain, so if anyone can tell me the signs of her pain or when we should let go, it would be very appreciated. It'll hurt a lot to let her go, but I don't want her to be in pain. This is my Roxy when she was younger.Thank you so much.

The decision about when it's time to let go is a difficult one.  Some people say that you will know when it is time you will know I have always struggled with the decision.  I am so sorry you are going through this.  Don't feel guilty about your family not being able to do anything for her I don't think there really is anything that can be done.  

If she is still eating and seems to be getting some enjoyment out of life then she probably isn't in a lot of pain.  If she quits eating and her lucid moments get very rare or non-existent then it is probably time but that is a decision for you to make.  You know your kitty better than anyone else.

Thank you so much, Denice. Your advice was very helpful. I appreciate it a lot.