What to do? Accept the fact that she doesn't like you which is okay because honestly her liking you doesn't seem worth very much. She sounds like an insecure, old bitch who doesn't have the emotional capacity to put aside her painfully low self-esteem for the sake of a postive work environment. You don't need someone like that in your life :)
You need to be strong and not let her bitchiness get to you. If I were you, I'd respond with a sly "I've had no complaints!" with a smirk then maybe add something like "It really doesn't mattter HOW you look, it's about how OLD you behave. I may look young but I act my age unlike you." That's what I would say. Bitchy people like her don't stop with their comments unless you get as fiery or more firery with them. I'd tell her that and if she keeps making nasty comments, then direct the issue to your manager and just try to stay away from her. At the end of the day, you're there to do a job. She's not a significant part of your life. I suggest putting her in her place then treating her like air and only interacting with her when you absolutely have to :)
She's just being petty because you look better than her. That's just being stupid.
But If you really want to change how you look to please her, put on some darker lipstick, wear more sophisticated clothes, maybe less preppy and girly, but if I were you, I would just ignore it. She's jealous and not worth your time
Yah sounds like she's jealous/insecure. Unless you work in a place that requires a certain kind of image (like if you dealt with customers at a high end accounting firm of something and had to be very business and conservative looking) then I wouldn't worry about changing your image for her. If there is a concern with appearances, then think critically about yourself and be mindful of the image you are presenting (types of clothes you wear, amount of makeup, hairstyle). But honestly if that's not a concern then just ignore her. It's a shame that people can be so petty and stuck up, but part of maturing and being a 'grown woman' is learning to ignore that stuff and continuing to be your own person despite what others say (so long as you are behaving and dressing suitably for your work environment). If it continues in a very negative manner tho, consider whether it could constitute bullying/harassment and whether your workplace has policies against that or not.