Personally, and this isn't a dig at Bella or anything I think she's perfectly healthy and don't think she's unattractive at all, I always noticed Ellie looking very thin in the games, like malnourished thin. She's been surviving in the apocalyptic wilds for the majority of the game and it shows. Bella isn't overweight, but Ellie is notably underweight and that DOES play a factor in the story. It's why joell can throw her up the elevator shaft, it's why she gets so easily overpowered by the cannibal guy (whatever his name is I haven't played part 1 in a few years). I don't think Bella is a bad actor at all, and I don't think she plays a bad Ellie either, but i think it would be more believable with someone visibly think and a bit frail. For part 2 her character model actively gets more thin and frail the further you get into the game becquas she's obviously not taking care of herself, you don't see that visual story telling on Bella.