Hi Claddagh
I'm really not that sure about the date of the first, round, photo. It's really hard to pin down a date with so little of the clothing and set showing. The only thing that pointed me to a date around 1890 was the little puff at the top of the sleeves. Do you have the actual photo? Is it possible to see it in full colour, or can you describe the colour of the photo and whether it's on paper or glass or....
It's possible the photo dates from the time of her engagement or marriage. She does look very young. I wouldn't worry about the difference in hair and eyes between the two photos - this could be due to anything from different photographic processes, to light-fading.
I think women have had pierced ears for thousands of years, haven't they - some ladies certainly never had their ears pierced (my mother and her mother and her mother all wore the annoying screw-on earrings - I hate them!), but others would have, I'm sure. If she came from a family of jewellers, it might have been the norm in her circle to have pierced ears.
The third photo you've posted definitely dates from the mid-late 1890s. This was the period of the leg-of-mutton sleeve, which grew to immense proportions just before 1900
The sleeves on this lady's top are certainly rather large, so perhaps later 1890s. In my opinion it is not the same woman as in the other two pics.
If you do have the original of the first photo (the round one), it might be useful to take a very high-resolution scan of just the brooch, and post the picture on the armed forces board. Someone there may recognise it.
Cheers
Prue