ok, let me get in here for a second- there are two reasons that she wouldn't attend on saturday, and you have to think about which one it is
1. as a religious jew, she can't travel on saturday and so she can't get to the location. that is not a trivial thing, if she simply doen't ever get in a car, and there is no way to get to the location without driving, then she won't be able to attend without breaking her position on her faith. if this is the case, can you find a place for her to stay that is close? that would be the correct comprimise - for the sake of her brother, she should be willing to discomfort herself somewhat - walk a long distance, sleep in a shitty motel, etc. that is perfectly reasonable. if there is no other option, then you have to think about that, too. if you are having your wedding someplace that is simply impossible to approach without a car, and this is the reason that she isn't attending, then she isn't being unreasonable.
2. jews don't, traidtionally, have weddings on saturday. if this is the reason she doesn't want you to, then fuck her.
3. you have to decide what is more important to you - to piss off your sister, and possibly create a tear in your relationship that won't be fixed, or to comprimise, I hate my sister. I tried to comprimise for my wedding, and she still tried to ruin it and pissed me and my wife off. so, if I were you I'd send her an envelope full of shit just to emphasise your position. but you could decide that your relationship is more important.
4. in 10 years, you probably won't see your sister very much, especitally if she is religous and you are secular. you'll talk to her a few times a year, and that's about it. you'll see your wife every day.
so, I lean towards the fuck you side