Get your taxes done using TurboTax

Since you are on the mortgage, live in the house, have the house as collateral and make payments, you qualify to claim credit. If the IRS asks, you can show where you are putting the money in to pay the mortgage. You will need to add her information as shown in the instructions below. Before you go to a lot of work, look and see if your share of the mortgage, property tax, charity, itemized deductions will add up enough to count. For most people, the standard deduction is larger this year. See How does the Standard Deduction differ from itemizing deductions?

A shared account means together you are paying all the bills. Only you two know who puts in how much and how you figured the amounts going in and for which bills.  The IRS does not want you claiming something you are not entitled to claim. You are both entitled to claim mortgage interest if the house is in both names. You are not required to claim the mortgage interest and most people don't. 

The IRS believes you should claim the part for which you pay. The IRS doesn't have much to say which makes it harder. The only thing the IRS says is what to do if you don't get the interest form, as seen  on page 11 of About Publication 530, Tax Information for Homeowners is:

More than one borrower. If you and at least one other person (other than your spouse if you file a joint return) were liable for and paid interest on a mortgage that was for your home, and the other person received a Form 1098 showing the interest that was paid during the year, attach a statement to your paper return explaining this. Show how much of the interest each of you paid, and give the name and address of the person who received the form. Deduct your share of the interest on Schedule A (Form 1040), line 8b, and enter “See attached” to the right of that line.