Rescued Chihuahua, Need Advice

Question
I found a 3.5lb Chihuahua roaming around the parking lot at work. They were predicting a major ice storm, so I caught her and took her home. Two days later I located her 'owner' but she said that she had gotten her for her foster kids to play with but 'she wasn't no good' so she 'had to put her out'. And she said if I could catch her, I could have her. Argh.  

Ok, so this is all I know for sure about her, she is at least 6 yrs old, she is spayed and he has had multiple leg fractures repaired with pins. I don't know the cause of the fractures, but I bet I could guess it was not too much love.  

She will let me hold her if I can catch her, but she is very fearful and timid. I can deal with the fear and that kind of thing as I have dealt with rescues before. I know it just takes patience and kindness for them to come around.  She isn't aggressive at all, and while she doesn't like my wife or I much yet, she is getting along well with the cats and our neutered male 11 yr old Chihuahua. Today it took me over an hour to catch her to take her outside for potty.. oh well, I needed the exercise.

So to the problems I don't have answers to. If she gets really nervous or upset (which happens frequently), she starts madly humping her toys OR she will bite her own self viciously on her legs. Very different behaviours, but seemingly both triggered by stress. Also, she will sit quietly with me if I hold her, but for no apparent reason, when she looks just as if she's about to doze off to sleep, she'll yelp like she's been hurt and launch herself off my lap. She falls asleep normally in her box, so I don't think she is in any pain.  If she hit the floor I'm sure she would have another broken leg.  I've been keeping her little harness and leash on her tied off to my wrist for couch time, but I would rather stop the problem, not just prevent injury.  

Thanks for your advice in advance!

Answer
Well some nervous dogs can safely be put on some types of medications that calm them down,but of course you would have to talk to your vet-alot of dogs are put on Prozac with great success

Also it wouldn't hurt to ask the vet if there's any dog trainers around that deal with nervous dogs