i'd probably personally feel that was a bit much, but it really depends on your sister and how she comes around. if she comes to you and becomes really involved, then take it at the time of your scan - but i'd probably not go there - just ask her if she'd want to see pics/video after - she may decide herself that she wants to be there as extra support for you - it's easier to deal with your emotions when it's not "in your face" and you have a hance to walk away without disrupting something IYKWIM?

i'm glad you were able to tell her without the rest of the family there - admittedly it was a quick discussion yesterday, but chances are, once she's had a chance to get used to the idea she'll come back to you and talk about not only your pg, but how she's feeling

good luck for your pg joy - i really hope it's a happy and healthy one, and that your sisster is able to be involved.