my sister is so triggering

we just got back from a vacation where i (17f) let myself have full food freedom and ate a lot. the whole time, she (21f) was eating just as much as me but kept making comments about how “big” other people were since we were at an all-inclusive, and about how i’m so much bigger than her, which she’s always done. i was already really struggling over the summer because i lost a lot of weight and then started eating again, and now she keeps calling me fat. everyone in my family has always commented on my weight, but they don’t think i lost it intentionally. as soon as we got home, she started talking about how she gained >!10 pounds!<, needs to lose it, and is planning to eat like >!800 calories!< a day. i told her that's like low but she keeps insisting she'll eat around >!800-1000!<. i’ve never told her that i struggle with this stuff or that i know anything about weight loss, so it feels really awkward and honestly really triggering. i don’t know what to say or what to do, because if i give her advice i’m scared she’ll lose weight, start commenting on my body even more, and get a superiority complex. at the same time, i feel like a terrible person because part of me wants to sabotage her, start competing, eat even less, and lose more. i honestly just want her to go back to college as soon as possible since she’s only home for the holidays, so i can lose weight in peace again without her triggering comments and not have to see her bc she's always making comments on my body.