My Sam is just 10 days younger than your little one and there is no way she could go without a day sleep....shes up at 7am. Sleep at 1230pm. In bed for the night by
715pm.....
Well done for feeding her this far along..... What does she do when you do leave her ? Cry, play, whinge ???
How much sleep is she getting in a 24 hr period ?

If you b/f her in her room, maybe feed her in another room, bright, curtains open, etc, let her have her feed, then take her to her cot/bed and explain that its sleep time. My DD takes a stuffed dog to bed, and has a bottle, so she knows those cues are for sleep. Your DD's cues are the breast. So maybe introduce something else (blankie, a book, a stuffed toy) that will prompt her little mind to suggest 'its sleep time'.....

I dunno if thats any help....but 18 months does seem young to have no sleeps at all (and no break for you during the day either....).

Good luck.