Los Angeles, CA modeling for a shorter girl could appear to be tough. A google search isn't that inspiring, but here are some agencies that have print modeling in LA, which are worth checking out.
I would also go to Barnes and Noble or a bookstore and pick up a booklet called CallSheet, in the magazine section under TV and Film magazines.. $10, you'll thank me later because it is a GREAT source for aspiring models.
As a new model I would aim high but remember it will take experience to work with the really great established agencies sometimes. You must have professional well produced photos and a compcard when mailing these agencies. So far I'd check out:
SWB Commercials Unlimited, 190 N. Canon Dr., Ste. 202. Beverly Hills, CA 90210
Avalon Artists http://www.avalonartists.com/
Don Buchwald & Associates
6500 Wilshire Blvd., Ste. 2200
Los Angeles, CA 90048
DDO Agency: http://www.ddoagency.com/about_us.php
The Daniel Hoff Agency
5455 Wilshire Blvd., Ste. 1100
Los Angeles, CA 90036
Talent Works: http://www.talentworks.us/twaboutus.html
Clear Talent Group: http://www.cleartalentgroup.com/contact.htm#
AKA Talent: http://www.akatalent.com/commercial.html
Arlene Thornton and Associates: http://www.arlenethornton.com/main.asp
Also I thought this post on YAHOO on LA Modeling Agencies was very helpful.
You can also find other agencies here. Make sure the agencies have a State license. This is also a list of agencies in LA that you could mail compcards to. Do your homework, research the agencies, find the best ones to submit to can involve work but if you want something the work is worth it.