Any bank will issue a few different types of loans on a house up to a certain percentage of the value of the home. The bank will send an appraiser to determine the value. Let's say the appraiser puts a value on the house at a nice round $100k. Then the bank will multiply the value by their percentage limit, each bank sets their own limit and it could be 70%, 80%, maybe as high has 90%. Let's assume it is 70%, so $100k x 70% = $70k total that the bank would loan out.
Here is the tricky part: if there is already a loan in place the the total amount owed from both loans is limited to the same $70k. So to answer your question, if she gave you seller financing then the bank would subtract the amount that you owe her from the $70k.
Here are two betterr ways for you to get this property and for her to get the cash:
1. Buy it from her directly with bank financing. This will require a down payment, but you might have a few options here. A 20% down payment is conventional. You could also try for FHA loan which has a lower down payment - I think it is 3-4%. You might also qualify for VA or USDA loans. Then as part of the closing, your bank signs you up for repayment and gives her the cash.
2. She could seller finance to you. Then you close and owe her the balance. At some point in the future you go to a bank to refinance the whole property. As part of that deal the bank will require you to pat off the existing financing. The ultimate result is the same: you get the property and she gets the cash. This might take a little longer depending on the banks policies.