Isn't it more appropriate to say "Wיhat is wrong with the small girl?" ?
Yes, or even "what is the matter with the little girl?" Report it and ask for your translation to be accepted!
plus does is have the meaning of something is with the girl? confusing.
The adjective rules are slightly different. Read this and it will be very easy to memorize the rules: http://www.nthuleen.com/teach/grammar/adjektivendungenexpl.html
You can also memorize a set of words for the second, third and fourth case. For example 3rd: Mit nach nebst samt bei seit von zu zuwider ausser aus gemäss entgegen gegenüber
If you memorize these and you use it in a sentence like the one above, it is really easy to apply because 3rd case belongs to "mit". But it is nicer to understand the rules :-)
It is a good chart, but there is a differece with other rules when there is not an article in front of the adjective. that chart say that we must add der-words, but there is differences only in Genitive with other charts -en, -er, en -er for male, female, neutral and plural and i am confused.