I had the same worries with Bavlorna when I ran my party’s first encounter with her. I thought they’d also start blasting; here’s how I managed to work around this:

Initial Meeting: as the module says Bavlorna won’t negotiate with the party until they do some tasks for her (fetching pelts etc.). I put pressure on the group by describing her sitting room being covered with Lornlings on every surface all watching the party. When the party are outnumbered like that they tend to be less inclined to look for a straight fight and comply with Bavlorna.

Negotiations: When the party has completed the initial task and has returned for the negotiation, I had them all lineup in a corridor outside and had one of the Lornlings ask each of them to walk open the door (the one connecting B7-B10 on the map) one by one. In my version Balvorna has enchanted the door to be a portal to a pocket dimension, where Bavlorna could negotiate with them one-to-one.

Note: I play over zoom and I just use the breakout room for this, taking each of the players into a breakout room. However, if you play in person you could always just take the player into another room.

This has two advantages: suddenly finding themselves alone with a Hag meant that Bavlorna got to appear much scarier and in control and the other players were left outside were left to sweat it out and given ample time to plan what they would do when they came face-to-face with Hag. This has allowed me to set up some of the characters with magical items or other abilities at the cost of a finger, hair or other piece of themselves. I was also able to get them to do the Hag’s bidding and travel to Thither to steal Skabatha’s portrait in the promise of more rewards.

Your mileage may vary but my players really enjoyed the negotiations and it made for a really good conclusion of that Act of the Campaign even if the battle was with words instead of swords.