This should be the meeting leader and/or instructor's role to politely inform the group that questions will be addressed at the end of the session or the end the end of a particular topic's discussion. It should also be that person's responsibility to, as politely as possible, admonish the offender as needed. Gentle reminders - 'Betty, we'll cover that in a bit' kind of thing. When/if the gentle reminders are not sufficient, it is still the leader/instructor's role to have a one-on-one conversation with that person.
It should not be the meeting or class attendees responsibility to resolve this issue. As a fellow attendee the best you can do is ignore the person and hopefully they will eventually get the message. Or, as quietly as possible so as to not disturb others if she asks you a question directly, flat out tell her you are trying to hear the speaker and then continue to ignore her.
You have to be tough with these kinds or the problem just continues to grow.