I'd be curious to see what she looks like as she gets older or from other angles. There's something about her that makes me think she might have something other than GSD or lab. But genetics are funky.
Also a lot of people can't recognize floppy eared GSDs as GSDs so don't worry too much about what a lot of other people say. Puppies can go through some funny stages as they grow up. Basically if it isn't an oversized Black and Tan GSD people will often say it's something else. I remember my dad once telling me white GSDs didn't exist and a lot of people won't recognize a sable either.
My GSD Shelby is at the very bottom of the standard but still in standard size. Somebody asked me how old she was and I said 3. They said she must be mixed because GSDs aren't that small. She's pretty obviously purebred though.