I'm not a lawyer, nor a trademark expert, so I also would recommend you speak to a lawyer, but...
" there was nothing to prevent someone from using a trademarked name in a completely unrelated field or industry (for instance, Delta Faucet and Delta Airlines) because there was no possibility that consumers would confuse one for the other."
Trademarking your name would not stop someone in an unrelated field from using the name, especially as the other party already has the name in use before you trademark it.
From what I can tell from looking at the other blog, although the names are the same, she is not in the same business as you.
To file the paperwork yourself (in the US) costs approximately $500. If you get a lawyer to do it for you, the costs can jump to several thousand dollars. In either case, it is my understanding that the process takes a minimum of six months from start to finish.