You should not be with someone because you feel sorry for them. It is very sad news about her mom. And a shame about her cat. ..
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Is there anything you like about her? You did stay with her for over a year. Do the bad things really outweigh the good? If you just don't see a future. Then sit her down and tell her you are really really sorry, but you just don't see a future...

I agree that you shouldn't stay with her out of pity. But can you remain her friend during this difficult time, and just be there for her as comfort?..

Angie's my yin...
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Why does everything have to be so black or white ? Why not wind it down slowly, over many months thereby creating the possibilty that you might remain friends even after the romance is done. It would work better for her, and will ease you off the emotional connection as well. A sudden break even at the best of times is traumatic, in her case it will be devastating, if you have any feelings for her (as a friend) why not take that into consideration. It's not pity, it's humanity...
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Carlos...

Is there any hope that you might want to stay with her and that you might have just hit a rough patch in the relationship? If not sadly i think you need to dump her now. Its going to hurt her especially with everything going on, but it will hurt no matter when you do it and stringing her along is unfair to both you and her. Maybe you can vow to stay friends with her because you obviously care for her and want to be there for her through this hard time...

This is a lose-lose situation...If you stick it out, you'll end up miserable, making her even more so...If you break it off, she might hate you for abandoning her...But I guess when push comes to shove you have to do what's best for you...Whatever that is, do it...However, if you could hold out until something positive happens in her life, I would definitely give that a shot...