Do not.....finish hee sentences for her. To me, it is so rude when someone does this. It calls into question the authority and power and control of my mind. You don't know what I'm thinking or what I'm going to say or HOW I'm going to say it. If a person wants to finish my sentences, then clearly they love to hear themselves speak so I stop talking around them. And with a stutter? It feels as though you're rushing me which makes my stutter WORSE. While as someone else said we aren't a collective so you should ask her (and even then, leave room for her to change her mind in the future if she says it's okay now but then hates it when you do it to her and wishes for you to stop), I'm strongly suggesting you do not do this with ANYONE. It shows a lack of boundaries and respect in conversation. Let them speak at their own pace.