Don’t hang the carer out to dry. Even if you feel there is very little you can do to support on a practical level, keep in contact with the carer (and also with the PWD, where possible) just to ask how things are going. Offer what support you can, even if it’s just a friendly ear. Families are so often terrified by dementia that they prefer to close their minds to the person living with it and the carer(s) affected by it. This is cowardly. And as @olddog said, telling the sole carer how wonderful they are does not cut it in any way!