As a secondary teacher I'd say it's way too early to make a judgement about her relative intelligence compared to other people. Maybe she'll be a brilliant academic, maybe she won't, but don't put her in the dunces pile at age 6. I've known kids who didn't really 'get it' until 14 or 15 and then suddenly a light bulb clicked on and they were completely different. Different children develop at different speeds.
That said, I really disagree with some pp's everyone excels at something/everyone has a talent idea. I've taught hundreds, probably thousands of kids, and honestly, I'd say it's the minority who are exceptionally good at something, whether academic or otherwise. Many many people are average academically, average at sport, average at art, average at pet care, basically average at everything. They can still be really amazing people and a joy to know, they can still go on to be well-rounded adults who have all the soft skills and great personalities, they just don't have one thing, or a collection of things, that is their niche that they're really good at. It doesn't mean they're failures at life, just that they are geniuses.
If I were you, I'd just carry on supporting her learning at home with the sorts of things I'm sure you're already doing (reading together, basic numeracy with household objects, talking a lot about the world around you etc.). And don't let her know how you feel about this. Celebrate her, praise her, and don't let her get an inkling that there's something wrong with her.