Home alone - too long?

Question
QUESTION: Because of the bus schedules, I am gone 12 hours a day during the work week.  I can't leave my tiny (2lbs right now, maybe 4lbs grown) Chihuahua unsupervised with my 2 bigger 11-yr-old dogs (the 9-lb one dislikes other animals and the 25-lb one is unpredictably tolerant of the much smaller puppy and is aggressive), so she will be alone even after she is paper trained.  Is it in her best interests to get her a friend her size (I've heard that getting one of the opposite sex, neutered at the right time, gives the best odds for compatibility)so she isn't alone all day?  I'm not really eager to get a fourth dog, but I don't want her to suffer.  Unlike my oldest anti-social dog, she likes company.

ANSWER: Sharon, yes, that is a good idea.  You can get another female or a male.  Two females will get along just fine.. One dog will end up being the Alpha of the little pack.
good idea!

---------- FOLLOW-UP ----------

QUESTION: Thank you.  At 4 months, she is already quite assertive in getting her own way.  My first female dog tried to establish her dominance with the second female dog, but the second one wouldn't listen and then grew bigger and aggressive, forcing the first one to back down and withdraw.  Is that more likely to happen when they are the same gender?  If the male is neutered before he learns to lift his leg, does that guarantee that he won't mark his territory in the house?  That is my hesitation about the male, but I don't want the fighting between the females.  Maybe the first situation was made worse because the first dog would be happier as the only animal in the house.  How often does that happen?

Answer
Hi-  a male will lift the leg LESS if neutered...No guarantees he will never mark the inside of his home.. If he does, it may just be a few times....
I would go with a female...that's just me..  No real reason behind it... YOU may want to take this question over to our Behavior experts...

Good luck