Modeling is more than fashion, and it is best to be realistic with yourself to get ahead, especially when it comes to getting attention of an agency.
Change your perspective in a way that works for you realistically to get an agent and to get work as a model. Whether you have a modeling agency or not, you need to know what modeling is and how you fit into the business before you start thinking about agencies and such.
Modeling is so many things these days, it is not just fashion. Do not get discouraged by not getting accepted into a fashion agency. It is sort of obvious that a fashion agency wouldn't accept a girl that is 5'8" so instead of wasting time, and getting a wrong perspective of what you need to be to be a model, why not look into areas of modeling that ARE good for you. Don't dwell on what you aren't and focus on what you are and where you CAN find opportunity.
Commercial print modeling is best for any girl who is under 5'8".
So you are not 5'9" and not tall enough to model with a fashion agency but fashion modeling is such a small percent of the modeling work that is out there. What about commercial print modeling agencies and commercial print modeling? What about modeling for accessories, beauty brands, shoes, handbags, fitness, hair, and body part model. Don't forget modeling is more than Fashion.
It is about finding an agency that is good for you and knowing where you FIT in the modeling world/business.
Hint: When it comes to beauty, it helps to have great skin and of course an event skin tone. And you DO need photos that show you modeling in ways you CAN model and your photos should look realistic to what you are honestly capable of. If you are 5'3" then there is no need to take fashion photos constantly, I would instead focus on creating photos that involve products, and create photos that look like ads for products that models of all heights can model. Think about it, models are needed for so many things...from computers, to tampons, to advil, to skincare, and the agencies that submit models to castings for these type of print jobs are commercial print modeling agencies and THEY DO work with models of all heights. For a list of a few see the agencies on the side of my blog or google commercial print modeling, print modeling, + your city. But it DOES help to send photos that represent print modeling, and do look like ads and editorials, and they are NOT so fashion based, more based on your personality and energy, and natural self.