Hi There,
My dd, Sophie has eczema that is triggered by a dairy allergy. She first showed signs of it when she was about 8 weeks old, by 12 weeks it had got so bad that dh and I were really worried, but after doing some internet reading I decided to cut out dairy (Sophie was exclusively breastfed) and low and behold her eczema cleared up. It took quite a while for it to go completely but we saw a dramatic improvement in 2 weeks. We have never really looked back. She is now 2 and is able to tolerate small amounts of dairy in her diet.
I would have thought though that if your dd fed with a dairy based formula and has never shown any signs of dairy allergy before then it is unlikely that she has a dairy allergy.
But as pervious poster said, it would be best to keep her off yoghurts for a couple of weeks then slowly reintroduce, keeping an eye out for any worsening in her eczema.
HTH
Claire