Hi Joy

i agree with the other ladies - it would be better if you told your sister a little before everyone else - maybe try and get together with her today or something? admittedly, she may struggle a little when you first tell her, but it's not that she's unhappy for you, it's more that's she struggling to come to terms with her own emotions

Don't try to "spare" her by not letting her know - it will just make it harder because she'll feel left out of things. good luck hun