How about this: you are not her job, you are someone she knows through her work.

You paint right? Is your painting "just a job" or does it carry a lot of meaning for you? Would it carry less meaning if someone bought one of your paintings?

Work is important. For some people it is the major source of meaning in their lives.

Also: you will lose her. There is no getting around that. All relationships end. But what she has meant to you is a permanent part of your life. I suspect what she was telling you in her letter is that what you mean to her is a permanent part of her.