Help me set boundaries with my struggling mom

[Anonymous]

Does anyone have a good book recommendation that helps to discern what is an appropriate level of emotional support to offer a parent, versus where to create a boundary? My mother has openly stated she sees no need for a therapist because "she has me," but it's really draining for me. I don't particularly feel like listening ad nauseum about how she has PTSD and has lost all her friends and being old sucks. At the same time I want to be a good daughter and don't want my mom to feel alone.