Bipolar Stepmother

Is it time to throw in the towel? I'm so, so sick of the repetitive pattern of always being on alert to see if she's in an okay mood that day, tensing up when she's in a bad mood, then cautiously relaxing a little when she seems to be smiley and happy again... I am 30 now and I still feel like a child around her, cautious, wary, anxious, always on edge and watching her every facial expression. My stepmother (who raised me since I was 9 so I consider her my real mom) was clinically diagnosed bipolar disorder about 10 years ago and it has definitely impacted our family. She has her good days, then bad, then good... but once she goes into a bad mood, it affects my entire soul and mind for days on end. All I want is to be on good terms with her like "normal" families, it doesn't have to be a super happy smiley relationship, I just want some sort of stability and calmness from home. Even after 21+ years of living with her, I STILL feel like I have to put on a sort of... show? scripted role? in front of her so I don't slip up and say something wrong to make her angry or pouty again. When she pouts or throws a tantrum, that shit lasts for WEEKS. And the emotional damage on all parties involved lasts a lifetime, building on top of each shitshow after another. When I'm around her, I try my best to think of how to please her, how to keep her in a good mood, how NOT to step on another landmine and tip her over the edge. Example: For Mother's Day, me and my sisters got her a surprise gift (Longchamp purse) and cards with cash inside and took the whole family out to a nice dinner and brought cake and wine. Her reaction? She was visibly moody and pouty all day, passive aggressive and silent, unresponsive to our attempts at small talk, then at dinner she was forcing out her thank you about the purse but her expression was dead and annoyed about something, and she didnt even open the cards we wrote her. But hey, what's new? It's been like this since as far back as I can remember, so I thought this was "normal", until yesterday I had a talk with my husband about it. He said "It looks to me like she isnt interested in trying to be too close with you, why do you keep trying to force it on both of you? I think it's best to avoid her as much as you can and only stress out about it when another fight actually happens, instead of tensing up ahead of time in preparation for a potential argument." He opened my eyes to the possibility that I *can't* fix her, I can't force her to be the unconditionally loving mother I want... she is her own person and she is too involved in her own demons to have the capacity for maintaining healthy relationships with her children. I sometimes wonder if some of her self-pity and victimizing herself mindset has rubbed off on me over the years, even though we arent blood related. I hate that we cant have the ideal mother-daughter relationship and I hate that I see some of her in my own personality sometimes. I'm really trying to not turn into her because I know how she makes others feel, and I hate it. Sorry for the ramble, I was just wondering if there are any other women out there who are going through the same thing and has any tips. Thanks for reading.