There’s a good piece of advice out there to never call a meeting when an email would suffice. This is mostly true. It’s definitely true when you are the person calling the meeting and you are the person who should be sending the email.
But sometimes the problem is not yours to solve, but rather you need Alice to talk to Bob, and that conversation just hasn’t happened. A meeting shouldn’t be necessary, because Alice could just pick up the phone or write an email, but she has not, and there is only so much you can do.
At that point, the dreaded meeting to “talk about something” becomes the tool you need. Once you set it up, the clock is ticking for Alice, and she knows it. If she steps up and reaches out to Bob, you can cancel the meeting, but if she doesn’t, then the conversation is going to happen.
If you’re facilitating this meeting, you definitely want to keep it short and have a clear agenda. The latter may not be easy because if you knew everything you needed, we wouldn’t need Alice to explain things to Bob in the first place. So in the absence of information, focus on the questions that need answering. It is entirely reasonable (useful, even) to have an agenda that is the list of things that need to be known, rather than the things that need to be told.