You may want to worm again in 10 days because from all I've read Ivermectin is not doing the job now I am going to send ths to casportpony since she is [to me] expert on worming and can help you figure out what to use and what dose, because if she is extremely wormy worming can really hurt them...
Okay not sure whats going on but a few questions, could she have eaten something toxic? has she ever been wormed do you have stagnant water any where she may have gotten into? you say she is eating but skinny which makes me think possibly worms. What do you feed and do you ever give supplements...