Final answer:
The pressure ulcer described is categorized as Stage II, involving partial-thickness loss of skin layers.
Step-by-step explanation:
The pressure ulcer described in the question is categorized as Stage II.
Stage II pressure ulcers involve partial-thickness loss of skin layers and may appear as shallow open sores or blisters.
In this case, the nurse observed full-thickness tissue loss with visible subcutaneous fat, which indicates Stage II.