My sister is speaking up about costs with being a bridesmaid... help!

Weddings are expensive. If $200 was the agreed upon amount, then $200 is the limit. Maybe that budget was also supposed to included alterations? With alterations, a $200 dress can easily turn into a $250-275 dress which is a lot.

As for other expenses, there shouldn't be any. Let her choose her own jewelry/shoes. If she wants her hair/make up done, that is her choice. If not, she can do her own.

Are there other expenses she is concerned about?

The only thing she has to pay for to be a bridesmaid is the dress. My girls got lovely dresses at David's Bridal for $120 during a sale. They definitely have some for cheaper. If she can't afford the dress and she doesn't want your help then she can attend as a guest. She has a year minus 8 weeks (shipping) to order and pay for the dress.

"The dresses I’m looking at are around $200 which is her cut off... I don’t think that’s unreasonable these days."

It doesn't matter what you think is a reasonable cost. You can't require people to spend more than they are able. The most considerate way to do it is to privately ask each attendant their budget and then choose attire that comfortably fits within that budget (including alterations). It's also important to keep budgets in mind with other costs you are passing on to them (shoes, accessories, etc.).

The issue of her not wanting you to cover some of the cost is a separate one and seems to be tied into the history of your relationship. I would handle that delicately and carefully pick your battles. If you are calling her a bully, she may be thinking the same about you (you say you are sensitive to her budget but you are also unwilling to compromise...).

Family can certainly be complicated. Good luck!

You need to ask all your bridesmaids privately what their total budget is for dresses (including estimated alterations) and limit your search to dresses under that amount. Then they buy the dress you pick. That's how this works.

$200 is a lot for a bridesmaids dress. I've been in two weddings, the first dress cost $60 and the second $120. My bridesmaids had options from $89-$169. I also didn't pick that budget until consulting all my bridesmaids. I let them pick their own shoes & jewelry so that wasn't an added cost, I paid for their hair and makeup (it was still optional, they could 100% do whatever made them happy and comfortable style-wise), my mom hosted and paid for the entire shower, and I paid a large portion of my bachelorette. All my bridesmaids were more than happy to spend a ton of money but I wanted to contribute since it was my wedding.