Yep, you can definitely get laminitis in just one foot but, as others have said, it occurs more commonly in both front feet or all 4, depending on the cause. I have seen laminitis in just the one foot mostly when there is an injury to one of the front legs/feet that means that most of the horse's weight is being borne by the opposite leg/foot, and they may then develop laminitis in this supporting foot - called "supporting limb laminitis". Glad your girl is back to normal today.