Yea, she looks very skinny. Have you seen her poop recently? I think that there is a good chance that she has internal parasites. If her poop is white and stringy then it's definitely parasites. I'm not a pro by any means, but in my experience most guppies that you buy from big box stores have parasites. Once you find out if her poop is white and stringy or not, then API general cure is something that has been very effective for me in the past with guppy parasites. Salt always helps guppies too.