So the context is about a football manager's wife. The person wrote the following about her
His Missus never left(Liverpool), and she's a bit of gold to boot.
What does it mean gold to boot, does it mean she's rich?
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To boot is an idiomatic expression used to emphasize something additional; as Macmillan has it,
used for emphasizing the last point in a list of comments or criticisms
The vegetables were overcooked and tasteless, and cold to boot.
The OALD entry marks it as old-fashioned or humorous, which I don't wholly agree with, but your quote is colloquial to be sure. I would "translate" it as
His wife never left Liverpool; moreover, she is a woman of independent means.
His wife never left Liverpool, and furthermore has some wealth of her own.
"She's" here is short for "she has", rather than the more common "she is". As Sarah points out in comments, "to boot" is an idiom that means "as well", "additionally", or "on top of everything else". One might have a bit of gold literally, which would generally be a sign of some wealth, or it might be figuratively (having money in the bank).
So it means "Not only did his Missus never leave Liverpool, she's also rather well off financially."