I am desperate for help and advice... Coming in as the new "step mom to be" apx 6months ago I have realized it's not so easy. 

The child is 13 now, very immature (still plays with baby toys, doesn't have hygeine guidance (her mother is NOT teaching her good things or enforcing them- nor is she a good role model in this dept.), we pay $450 a month in child support and the child comes over every other weekend and only has rubber clogs for shoes, no warm jacket, etc.  (She isn't "allowed" to bring other shoes, supposably doesn't have any- when she did wear her "school shoes" over one weekend she got into trouble and they were KMart, velcrow sneakers that were demolished.) 

One of my biggest concerns is her eating habits.  She REFUSES to eat bread, hamburger, etc.  She ONLY eats hot dogs (cold and cooked), chips, candy, cookies, chicken, bologna, pizza, etc.  She won't eat milk in her cereal and will only eat cereals such as cocoa pebbles or fully loaded sugar foods, if we run through somewhere while we're out for lunch she will only eat a large frie and then want candy or cookies... she literally is in some serious danger!  It's absolutley crazy!  I don't know what to do!

We are now expecting a baby in a few months, she refuses to "grow up" or mature in any way and her mother supports this, she won't eat properly and tells her mom we don't have food here for her, she wants to lay on the couch and watch preschool aged cartoons and play video games- we can't get her to play a bord game with us or card game.  She is scaring me and for the sake of the new baby I can't get over this behavior and situations. 

Can someone please help.  We can't afford to live off the $800 a month we get and her mother gets $450 from us for support alone and the child needs obvious help in many areas... I don't know what to do... Please, Please help me!

There are no guarantees in life, but as i read the paragraph below it seems as if Dad may fall within the guidelines. It's worth a try, and you could do this without an attorney.

"A petition to modify the child support order may be filed by either party to a support action if a material change in circumstances has taken place. One example of a material change is the loss or change of income or employment by either party. The Domestic Relations Section (DRS) of your county court is responsible for determining whether or not a material change in circumstances has occurred. To file a Modification Petition, contact the DRS that manages your case, and request a petition for modification, complete the petition and return it to the DRS. The DRS will advise you of its determination and if and when a hearing will occur."

As far as the chocolate milk--I'd wiggle here. There is ovaltine, which has some vitamins, and hershey makes a syrup with extra calcium. See if you can compromise, use half of what it says on the package. Buy gummy vitamins. They taste like gummy bears. Be sure you keep them hidden or locked away so she doesn't eat them like candy.
On SnglDad's suggestion, things may be called by different names in your county but it seems reasonable to me that your local laws would have a similar statement. Call the family court and find out.

Thanks again... you are right, they do have that option at Dom Rel here, locally... We are trying to get legal advice before persuing because mom will have an attorney and we can't afford one- we also dont want to attempt any changes or cause any more fuss without serious chances of something productive coming from it. We just don't want to be the people that keep taking someone to court for stupid reasons (or to some may be stupid reasons) and just making more of a mess of the situation rather than going prepared and knowing what our possibilities and outcomes might be. Thanks again everyone! My nerves are calming with advice and support from others!