Read the instructions to the I864. This situation is discussed there. Talk to an immigration lawyer.
The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter,not should it be viewed as establishing an attorney client relationship of any kind.
To use your assets I lieu of income you must provide proof of them and having them for at least on year. The ratio of assets is 5 to 1 meaning your 79 k calculate to be less than $20,000. Which may not be enough for her support. You can always have someone else to co sponsor her.
Your question underscores the necessity of having excellent counsel represent you. Do not try to do on your own--don't file any forms without an attorney. See Part 7, use of assets in the instructions to the I-864.
No attorney-client relationship is created or implied by this communication.