rescued cockatiel needs to gain weight

Question
Thanks for the advise for this little lady.  I have another question about her depressed state though.  I have put her in a larger cage now with toys and perches, etc.  She still is depressed, though she sings a little from time to time.  She is physically healthy but mentally, I am not sure.  Poor thing is very depressed and stressed (from the ferret torment).  My question now, should I look into getting her a friend to keep her company? and if so, a male or female and a youngster or adult a few years old?  I want what is best for her and since they are flock animals and I can't spend hours per day with her (though I am in and out throughout the day) I was reading that a cagemate might be what she needs.  What are your thoughts on this.
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-----Question-----
I have just acquired a female cockatiel from a bad situation (for the bird). The original owner gave the cockatiel and a ferret to "Rita" and "Rita" has had them for several months.  The ferret has tormented this poor little lady so she would hiss and screech and is/was just plain unhappy.  Now I have her and plan on lots of quiet time and plenty of TLC when she gets acclimated.  My question is what is the best thing to help her gain weight.  I am guessing the stress of her life is what has made her skinny.  She is underweight (I can tell from comparing to other tiels.)  Anyway, should I just give her a regular, good cockatiel diet with fruits and veggies or is there something special I should do for her.  I just got her today, so she may gain on her own with her new, quieter surroundings.  She is actually singing already, something I was told that she didn't do.  That is a good sign.
-----Answer-----
Hello Donna.  Thank you for your post.
First of all, you need to take this poor little lady in to a Certified Avian Vet for a wellness check.  Let's make sure that she is healthy.
If she is already singing, then, yes, that is a good sign.  If you try to put weight back on her too fast, it could actually kill the bird.
Start off with smaller amounts of food and gradually work up from there.  Definitely offer fresh fruits and vegetables, and try to get her to eat pelleted food instead of seeds.  Seeds are high in fat and that is really hard on a bird's liver and kidneys.  You can mix a little bit of seed in with the pellets, but only do this until she will eat the pellets.

If you have any other questions, please don't hesitate to ask.

Good luck and God Bless.
Dianna

Answer
Hello Donna.
It's going to take some time for this little lady to get over the torment from the ferret.  Much like if you had been bullied and tormented for a long time.
The fact that she's singing now and then is definitely a good sign.
When you are not home, put some soft music on for her, or some Nature's Sounds, especially one with birds in the background for her to listen to.  Also, make sure that she has at least one or two toys in her cage with bells on them.  She'll love to play with the toys and ring the bells.
Right now I do not recommend getting her a friend.  She is still too skittish and afraid, and this may only make her worse.

It does sound like you are doing a great job with her.

Please come back if you have any other questions.

God Bless.
Dianna