Is my mare simple of mind?

i bought a mare from a feild (felt sorry for her) as she is in very poor condition, once got her back to the yard i kept her in for five days for worming then put her in the field the other horses ignored her (very unusaual as mixed herd) and if any one went near her another mare attacked them it was though she was looking after her, her eyes seem dull and lifeless and follows me around the stable when i go in there, but when i leave she screams (this makes me cry) also her top part of her head seems larger than it should be and the bottom part seems smaller, she is a welsh sec a and 3 years old, she craves human company , it is really hard to explain but the only way to explain it is that she is like a disabled child, i have the vet out physically she is in good health although she twits front left when at walk to a point her shoulder juts out( under vet for this), could she be of simple mind through neglect or birth deformity.