Mel is clearly struggling with the hunger in there, and I can understand the misery we've seen from her since the teams split into two in order to compete for immunity. It's clearly having a physical affect on her - not just in her gaunt looks, but she mentioned feeling some pain and breathlessness when walking up the steps. These factors would have a negative impact on most people's mood.
Her campmates are more than aware of her irritability and now seem to find her difficult to approach, particularly on the subject of food. I'm not sure whether they're putting up with it because they can understand where it's coming from, or whether they feel that's how she actually is and want to avoid conflict with her.
When Edwina was discussing the octopus with Vicki, it was telling that Vicki tried to stop her from saying anything and told her it was best to leave it and say nothing. Also, Nadia commented when she came out that there was noticeable tension around the evening mealtime cooking, as though it's a regular occurrence that everyone is treading on eggshells around Mel.
It can be uncomfortable viewing at times, but she clearly has support from people voting for her, since so far, she hasn't been in the bottom two, even when there were only four of them to vote for.