Breaking up with someone might cause them pain, but it doesn’t make you a jerk. This is a tricky situation, with her friend passing. On one hand I understand that you don’t want to break up with her at such a time. But on the other hand, you must be careful that she doesn’t rely on you for emotional support through this, which may only strengthen the bond she feels to you and make the eventual breakup all the more difficult. You should keep your distance from her and break it off as soon as a reasonable opportunity arises.