If the kid has already experienced 1.5 years of gifted ed, the first question I would ask is, "How is that going?" If she's keeping up, finding it engaging and interesting, then it's an appropriate placement, and I'd stop worrying. If she's showing that she's struggling, then one of many factors I'd be looking into is whether the EG result was way off. But I'd also be looking at whether she's disengaging due to boredom, which would indicate that the EG result was at least reasonably close, and as EG usually indicates, she needs more.
Another thing about girls is they're notorious for hiding extreme abilities and attempting to blend into their surroundings. I have an HG 9yo who did just that.
A hothouse environment only exists if the parent is actively hothousing, because it's an action, not an innate property of the child's surroundings. You can create an enriching environment, but the child will only engage in it if they're intrinsically motivated (strong indicator of giftedness, but not entirely necessary, as it also involves individual personality, plus environmental factors like how the activity is presented and/or the behavior is modeled by parents) or coerced into it (hothoused).
For example, our DD had access to books from infancy, so they were there, and available, as one feature of an enriching environment. But DW and I never brought DD a giant stack of them in her toddler years and told her to quit what she was doing and listen to stories. She brought the stack to us, unasked, and she had plenty of other activities to choose from.
A common cause for doubting parents is when their view of normal is askew, due to lack of experience with children of that age level who are closer to the middle of the distribution. This happens more easily than you'd think, because we tend to cluster around family (genetic links) and friends (self-selected peers). I note you don't identify the stay-at-home parent who is an experienced educator... if that's not you, then I'd be very interested in the other parent's opinion, if they've taught this same age group and/or had gifted education training, because that parent would have seen a lot more "normal" and have a better calibrated frame of reference.
This happened in my own family. DW was teaching our DD the things she thought she ought to know based on her experiences caring for her nephews, plus the expectations of a school system in another country that was much more rigorous. This is what set her parameters for "normal." But as I watched DD acquire the required skills for K in the US before she turned three, I was constantly asking DW, "What are we going to do with her when it's time to go to school?"
