I can tell that you, the thread starter, are a daughter who cares about her parents.
Literal
Thread-starter-san [subject-が] parent-caring daughter-san is [nominalizer-こと] [topic-は] understand.
Online forum language. トピ主 (thread starter/OP) is internet slang — トピ from トピック (topic) + 主 (master/owner). 親思い (caring about one's parents) is a compound adjective. であること nominalizes the whole identity claim. The polite さん on both トピ主 and 娘 shows the commenter's courteous tone.