How to maintain my joy / peace around mom who seemingly isn’t in a happy space

Dear Coach C!

Last weekend my husband, son and I went to my parents’ cottage with them. My mom was in a mood that was not light to be around (my guess, because I know her so well, is we were all with my brother who is not the brightest star in the sky and she has always seems to have some negativity after being with him) I used to allow that to bring me down too. It’s definitely not affecting me like it was . . . but it still has an affect. I’m trying to apply your teachings but I’m coming up short and need some help.
I understand that I can be happy and in peace regardless of where others are at. This has taken a considerable amount of time for that understanding to sink in. However, what does this mean as far as putting myself in her (mom’s) presence again soon? We were going to go back to the cottage this weekend. (It’s EXTREMELY small). But, I find myself not wanting to go because of finding it difficult to be around her when she’s like that. I know I can just love her (at least I think I know this!) . . . but what do I do about choosing to put myself around her when I could choose not to and do something that I know would be lighter and more fun for me? And, I should add, that the main reason I want to go to the cottage is my 3 year old son LOVES going there. He repeatedly yells out when we’re there, “I’m at the cottage! I’m at the cottage! This is SO fun!”

Thanks so much, Coach 😉