The Chicago Manual of Style's general rule is expressed in section 9.3: “In nontechnical contexts, the following are spelled out: whole numbers from one through one hundred, round numbers, and any number beginning a sentence. For other numbers, numerals are used.”
They also say use numbers when refering to dollar amounts: $34.56
And spell out numbers in dialog as they would sound if spoken: Sixty-three, one-twenty-nine.
Bottom line, as long as you're consistent ands it doesn't look funny, it's fine. Your editor will adjust to whatever house style they use if she feels it's required.