In Session 7 the Doom Slingers found the Delerium River sent them for and made a hasty retreat.
After breaking the large delerium crystal while removing it from a chunk of meteoric iron, River has asked the Doom Slingers to replace it with an even larger crystal rumored to be beneath the Rats Nest Tavern. She paid the full price for the crystal she broke, offered a bonus for the rat's nest crystal, and is in a hurry to get it. She obviously knows something she's not telling. Maybe she's feeling some pressure from the Amethyst Academy.