Looking at her picture, it just looks like that is how she was built. She's not overweight, is not an obvious "wow, look at that crest", and some of it is muscling. If you think about it, stallions who end up getting a lot of muscling just from being a stallion, has a big crested neck, its nothing bad, its just the extra muscle they develop in their neck. She is a cute looking horse, and I wouldn't worry too much about it, unless it becomes very obvious, or she starts showing signs of other health issues. As for the swollen lymph nodes, if they don't get any bigger, and she doesn't end up getting a running nose, or other symptoms of being sick, then I wouldn't worry about that either. Again, it could just be the way she is, or maybe her immune system has just kicked into gear over something, so you are noticing it, but it isn't really an issue. Just keep an eye on it, and make sure that it doesn't get any bigger or anything.