Fashion agencies invest in their models. Putting money up for their compcards, housing, and portfolio needs.
Commercial Print modeling agencies do not. While a commercial print modeling agency is where a shorter model will find opportunties, she needs to have the right photos, the right mindset, and ambition.
Don't be mislead thinking modeling is easy. It isn't.
For a petite model understand that a commercial print modeling agency should be your goal and also understand the work that is involved after you mail your photos and get the agency meeting.
Commercial print modeling agencies -yes legit ones- will ask you to get your compcard together and portfolio. You will be advised on what to do, and the photos you need, but really it is a "figure it out yourself pursuit, and a trial and error pursuit."
Be prepared to do the work and make your compcard, give it to the agencies and be more in control of your pursuits.