I assume she means to bring him as an assistant photographer, no? Because there's absolutely no reason why he should be attending as a regular guest.
I think it's absolutely reasonable for her to request to bring him along as an assistant.
But if she's only charging $100 for the entire night, AND her editing services after the wedding, I'm going to go out on a limb here and guess that she has no idea WTF she's doing and probably thinks she'll get to socialize with him as if they were normal guests at their own friend's wedding. In which case I think you should (a) tell her no, and (b) look into a backup photographer or at the VERY least ask your loved ones to take lots of photos and send them to you, because I have a feeling you're going to be very disappointed by this person's work.
ETA: You said she wants to bring him along to hang out with him? WTF did she offer to photograph your wedding for, then, if she just wants it to be hangout time? Sounds like she's looking for a free Date Night with Hubby, frankly, where she can collect $100 and get free dinners. I'd tell her no to the husband, then look for another photographer because she sounds incredibly unprofessional.
You also said he's her ride. If it's something where they're coming from an hour away and he'd be sitting in the car all night waiting for her to finish "working" ... then yeah, sure, I'd let him come in and eat dinner. But that also means she'll probably be talking to him all night rather than working.
And for $100 I'm also going to guess that she's either a professional doing you a MAJOR favor here, or (more likely) she's a crappy photographer with no editing skills. Because even very basic, newbie professional photographers would never charge as little as $100 for wedding photos.