I think being upset is valid, I'd be pretty pissed myself honestly, but at the end of the day you probably can't do much. I second @Celia though, that seems weird and like there's Definitely something else going on. Have you guys talked about WHY they chose that day?
Also, if you already sent your STDs out, then if guests do end up having to choose which to attend, there's a good chance they'll pick yours since they knew about it first, if that makes you feel any better...
But I agree, it's pretty shitty of her to pick that day. There isn't really much you can do about it, but honestly if I were invited to her wedding I would seriously side-eye her, and possibly not even go
I'd be upset. Has she booked a venue? Has she really considered what this would mean for guests? A 3 hour drive between yours and hers doesn't sound fun.
As a guest, I wouldn't be happy about back to back weddings. I'm usually dancing all night, so my feet hurt the next day (and it's a really fun wedding, I might be nursing a hangover). I'm not sure I'd go to the second day if I got the information about the first earlier.
Also, is she planning on having you as a bridesmaid or is she one of yours? No way could I be in a wedding the day before or day after mine
I would just imagine your families and mutual friends would be exhausted. I wouldn't be so concerned about the thunder stealing but just the whole ordeal. My sister is my other half and my best friend, I'd be like "Let's just double up and have one big shebang!!!!!" Am I weird?