You might find this useful: http://esl.fis.edu/learners/fis/german/kasus/caseTables.htm
Missing here on other side of Pacific also. Looks like disappeared in 2016. But available via wayback machine: https://web.archive.org/web/20161120002014/http://esl.fis.edu/learners/fis/german/kasus/caseTables.htm
And there you go, in German it works to say its rice, because "das Mädchen" is neuter and could own rice. The problem comes when you translate to English, because the girl is feminine. Yet, in children's stories you will find animals with food that people eat such as in Goldilocks and the three bears. So, maybe there is a story out there with food that is designated as "its rice". Who knows? Of course, in that particular story, the bears are actually given genders: Papa Bear has his bowl, Mama Bear has her bowl and Baby Bear has his little bowl.
Lolz to the whole question, but to explore it...yes to 'THE baby bear ate its rice', but 'Baby Bear' without a 'the' is a very specific bear with a name, so to me it must have a known gender. It jars in the way 'Rover ate its dinner' does, but 'the dog are its dinner' doesn't.
The other way around is true: if you have a word with ß in it and you are typing on a keyboard without that character, it is good form to replace it with ss (of course, if you have the ß symbol then you should always use it appropriately). Or if you are writing to a Swiss-German, they do not use the ß. However, as with everything, there are specific rules for proper use of s, ss, and ß in German-German, and in this case, the word is certainly "essen."
That would be "ihren Reis". See the possessive adjectives here: http://www.germanlanguageguide.com/german/grammar/possessive-adjective.asp
The one you're looking for is accusative case, masculine noun.