Boss can't stfu!

My boss cannot shut the fuck up. Every time I make the mistake of inviting her to a meeting, she takes over with long soliloquies and makes it nearly impossible to use the meeting for its intended purpose e.g. to discuss project deadlines. I have tried talking to her about this, and she says she knows she can be garrulous, but then she can't seem to help herself. The problem is, sometimes I do need her support in meetings. Any thoughts?