Wow! I didn't know there was a bella in sims 3! I gues I'll have to look for her! Lol. I recently got another sim that I like. Gobias Koffi. If you change his bald head in the mirror and give him a better looking shirt, he doesn't look that bad. He actually looks kind of cute. Anyways I'm going to try and find Bella right now! 
They live in Sunset Valley. There are other references to Bella in the Sims 3 including:
Bella appears on the cover of The Sims 3.
There is also a book titled "Murder in Pleasantview" by Alexander Goth (though it could not be the as-yet-unborn Alexander from The Sims 2 unless time travel is involved), which could hint at an explanation of Bella's disappearance between The Sims and The Sims 2, given that alien abduction is not present in The Sims 3 base game.
When you look on the book case, there is a picture of what looks like Bella from The Sims 2.
If a Sim has the Good trait, one of the charities they can donate to is Bella Beneficiary.
When a Sim is sketching at the drafting table, he or she can sketch a black-and-white picture of Bella from The Sims 2, in her signature gown.
When a Sim paints a small painting, one possible picture they can create is of Bella, wearing her signature red dress and with her back turned, near Cassandra, who is in the white shirt and blue pants she wears in The Sims. They appear to be among gravestones (which makes sense for the Goth family), although it is hard to be sure because the picture is painted and texturized. A large painting, which is the one above Mortimer's bed in The Sims 2, can also be painted. Another large painting includes a couple on a balcony, The man wears a suit and the woman wears an elegant red dress, which indicates that they could be Mortimer and Bella.
