gender reveal/baby shower ideas?

Ok my sister is right now almost 11 weeks and my mom and I are wanting to to host her a gender reveal party but nobody wants 2 different parties so i am trying to figure out how to do it all together... like i am thinking letting all the guest know the gender but keep it a secret from my sis and letting her open a box with balloons come out as just a simple reveal for herself. I am thinking doing this when she is 25 weeks so she doesnt have to wait TOO long to know the gender but not TOO early for a shower. I had mine at about 25 weeks and glad i did cause i had preterm labor from 30 weeks until i had her at 36 weeks.... i am just looking for any sort of ideas for this open to any and all suggestions. Thanks :)