One bm left out of Bachelorette?

5 bridesmaids, 3 in different states. 4 of the 5 Are in college. I knew going into this with the girls i had i probably wouldnt get a bachelorette party and i was fine with it, im not a drinker or party person anyways! Wedding is on a Saturday. Two girls are flying in Wednesday, and one is flying in midnight on Thursday. The other two will be around starting Thursday. So Friday is the first day I'll have all 5 girls together, so I figured since we couldn't do a bachelorette we could do something fun in the morning like an escape room before decorating the venue and rehearsal that night . I'd told this idea to all of them and they seemed fine with it.

Then, 1 bridesmaid messaged me and told me her and my two MOH (my sisters) were planning a surprise bachelorette party on Thursday. I thought it was so sweet they wanted to plan something! She was saying he plan was to dress up like flapper in the 1920s and do a 20s themed escape room and go out to a fancy restaurant.
Buttttttttt the issue is they are planning for Thursday. And the last bridesmaid, K, isn't flying in until Thursday night, so K will miss it.The other girls wanted the party to be a surprise but they decided to tell me because they wanted to know if I would be upset since K can't come. I feel so torn. I did already tell them it was okay to keep planning, so I guess it's happening. I guess I just don't know how to tell K that she's going to miss the party. I don't want her to feel bad. I care about her a lot, but I do want this party. She's reasonable so I think she will understand. I'll just have to make sure she feels loved and included on Friday when she is here. Any advice on how to go forward and potentially smooth this out?