Wendee
I don't think that doing soy formula and soy milk will be hard on her system - it may actually be better to slowly decrease the formula and increase the milk (over a number of weeks) than to just switch like you have...might give her system more time to adjust.
Re the yoghurt - I am guessing here that it works the same, but my DD used to be on soy, is now on cows milk - and she tolerated cheese and cows milk yoghurt long before she tolerated cows milk itself - I assume it would be similar with soy...worth a try anyway, you can always stop it if it doesn't work for her. The reason I doubt the soy milk is a total allergy is she was doing ok on the soy formula....I suspect she needs a much slower adjustment, but it certainly couldn't hurt to have her tested.
I think it seems like you are facing a number of issues
1/ digestive issues possibly including hunger
2/ teething - the gnawing on hard foods, pain relief helps etc
3/ some seperation anxiety
So I think you need a 3 pronged attack on this. Work on getting her to eat more during the day, use some formula if you can, will probably fill her up more, but mostly work on solids.
Treat the teething with teething gels/tylenol/teething powders
Work on building her trust - to be honest, my dd still likes to see us at least once each night also, some kids are like that...but if you can work on her trusting that you will always come, then she should settle more quickly when you do, and gradually require you fewer times. This one will be harder for you with the biomum issues and what not. My DD used to call us in (by crying) several times a night, after SA kicked in, now we are once most nights, and sometimes not at all. When she is sick, or teething, dh often ends up sleeping with her
, like right now, she has an ear infection.
HTH.