<human>: This is NOT a joke. My girlfriend (F19) has been with me (M21) for 8 months now and when I asked her what she wants to do when we've graduated from college she says she wants to be a mermaid and that mermaids exist and that she will one day turn into a mermaid. 

I didn't think much of it and thought she was playing. But then over the months she's continually brought it up and it seems she is very serious about this so-called "ambition" of hers. I don't know what to do, because everything else about her is normal and I love her apart from this really weird thing.

Summarize the given text in a few sentences.
<bot>: How do I convince her that it is never going to happen or shall I just let her continue with her delusion and just suck it up and ignore her one fault?.