Hi, getting a baby to sleep in hot weather can be a pain! At least your bub will sleep without being swaddled! My DD was swaddled (& needed to be as she'd wake herself up otherwise) but it was a real challenge in summer to keep her cool enough. Seems as though you're doing the right things though - fan and minimal dressing.
Anyways, regarding her NW, just a few thoughts: have you ruled out a growth spurt? Sometimes you'll get a week or so of NW for hunger and then they just go as fast as they started. Also, now that she's 4 months, have you considered moving her to a 4 hour easy during the day? Being on a routine for a younger baby might be causing the problems at night? And finally, maybe if she's just eating for a few minutes and then settling again, you could just give a sip of water (if you don't want to nurse for fear of comfort feeding) and see if that satisfies her 'thirst' and maybe after a few nights the NW will go as she knows she's not going to get fed?