Everybody grieves at their own pace and it sounds like your sister is also wrapped up in not having someone during the holidays whereas you do.
You offered a reasonable invitation. Maybe offer a second, equally reasonable invitation to do something else which isn't family. E. g. offer to go see Rogue One
with her on the 28th, something like that. Invite your boyfriend along, or not.
If your sister rejects this invitation as well, then wash your hands of it as you will have done more than enough.