My fiance wants to have a friend of his who I'm acquainted with to be a bridesmaid. I'm okay with this; she's very nice, and if we didn't live so far apart, I'm sure we would be friends. But who should ask her, him or me? I would feel uncomfortable just calling her myself.
You have two options. Either you ask her together -- write a letter or send an email from both of you -- or he asks her to stand up for him, since she's his friend. If she were to be a groomswoman, she could wear the same dress as your bridesmaids or something that complemented their attire but showed that she was on the groom's side (even a tux!). She might feel more comfortable standing on the groom's side because she knows him better, and your attendants should be the people closest to you. On the other hand, since she's a close friend of your honey's and may soon become one of yours, having her as one of your bridesmaids might be a good way to open up the door to a friendship between you. It's your call.
Your Bridal Party
Choosing Wedding Attendants