All the grease spell did was act as a stimulating lubricant.  That took away the friction of the soft spongy texture of the creature.  As it rubbed against her.  Rubbing her nipples now into a taunt hardness.   All the while the creature continued to fuck her.    It is not long before the dwarven tantrist is screaming with a orgasm that suddenly strikes.  As her own juices bath the tentacle impaling her.    Yet the tentacle doesn't seem to be stopping,  as it continues its assault on her.