Her nest was in the ruins of Thyr Morgan, in caves under the city. She had laid many eggs but unfortunately for her, she was also in possession of some loot.
The party initially tried to grab and run but it went sideways quickly. Mordus Silverstone in his briliant lightbulb moment grabbed one of the nestmother's eggs when the party was escaping he lair. Little did he know that she would want it back.
Latter in the Thyr Morgan Outskirts the party was attacked by the nestmother again. Seemingly following Mordus for no apparent reason... she wanted her egg back... and was killed in the end.