You can wrap a box and put the color of balloons inside and have them open it
You can buy a cake with the color inside it nd have her cut it to let everyone know the gender.
You can take her with you to the u/s
She's 93 and my appointment is an hour away or I would take her with us. I think we are going to do balloons or something similar. We did the cake thing with my first and want something different this time.