After you mentioned the good qualities of another female, and desire to have a female like such.
2 Answers
The word 'catch' is used figuratively. It implicitly compares the person to a (good) fish that one has caught. A related use: He | she is 'a keeper', that is, not a fish that one would toss back into the water. A fish worth keeping.
http://www.merriam-webster.com/dictionary/keeper?show=0&t=1419169461
When words are used figuratively, over time the underlying meaning is often forgotten, so that a person who uses these words might not be aware of the basis for the figurative meaning.
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1Indeed, dating terms are full of fishing / hunting metaphors, such as fox to mean "attractive person" and websites named Plenty of Fish. Commented Dec 21, 2014 at 19:53
She is just saying that, from your description, the girl sounds like a perfect find, for dating or marrying.
catch - (noun) one worth catching especially as a spouse. Merriam-Webster
answered Dec 21, 2014 at 12:47
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Or for other stuff, depending on the context. (And there is, of course, always the danger that it's said sarcastically.) Commented Dec 21, 2014 at 18:52