Good that their stopping for you. Are you going in your head to think what to say to her next? If that's what's happening (it happens to me a lot) that'll probably be what's stopping you being able to continue to flow in convo.

You'll be expected to take the heavy lifting of the convo at the start to give her mind time to catch up with what's actually happening. Just keep talking. If she's responsive then she'll start contributing to the convo and it'll get easier.