Congratulations on being a GG! We threatened my DIL that if she didn't tell us (her Mother and I), we would storm her house and find the envelope that has the info. of what she's having. My DIL said she didn't doubt us for a second.
She had a fun reveal party...we had a blast and are expecting a baby girl in August. Perhaps you can entice your GD into having a reveal party since most women are always up for a party! A party might be more attractive to her than being secretive.
I can't fathom why some choose "gender neutral" for a nursery BUT that opinion IS coming from "old school" and had no other choice kind of person.
Here's what I made when faced with a gender neutral baby quilt a while back. I didn't use a pattern, I just cut as I went, adding wherever I liked and quilted whatever I felt like ...out of "gender neutral" constraint frustration.