I recently went to a site that said that Tiara was a brown maynx. Is this official info, or is it fan-made?
As noted on the news page here, there's plenty of information being revealed concerning the canned Sonic X-Treme. That includes information on Tiara. Quoting from the topic on Tiara:

Tiara is a Manx kitten. Originally, she was slated to be a bandicoot (look out Crash!)... but in comparing the real animals, my pick is the Manx, mang!

Read that topic (and the message board) for more stuff as it's not necessary to ask here to get it second hand. --True Red