My dds were a lot like you describe your dd at that age except that neither of mine had early gross motor skills. My dd11 actually had somewhat slower than avg gross motor skills & dd9 was pretty average. They were both early potty trainers, too (16 and 20 months respectively), but I don't know if that is related to giftedness or just my being lucky
!
Both of my girls were speaking in sentences at 18 months like yours and both started using single or two combined words btwn 5.5 to 6 months. Neither of my girls is PG (profoundly gifted, Davidson Young Scholars level), but one of them at least is HG (highly gifted).
Like others, I'd assume based upon better hindsight than foresight and the similarities btwn your dd and mine, that she is probably gifted. I had no idea that I had gifted children until my oldest was 6.5 or so. I don't think that it did them any harm for me to not be doing anything special when they were that age.
It sounds like you are an active involved parent who is offering a lot of great experiences for your dd, like the museum, so I'd say that you really don't need to worry about anything more at this point. In our experience, the worrying begins in ernest when they start school if you choose to send her to elementary. Kindergarten really wasn't an issue. Both of my dds had fun in K.
1st grade was hard for both in different ways and we wound up homeschooling dd11 for part of 1st. I've heard that from a lot of parents of gifted kids -- 1st is a hard year due to the major focus on reading and things that gifted children often already know well.
