I would recommend that you speak to a lender and get pre-qualified for your own loan. That will give you the information that you need so that you will know if you are able to assume her loan. Interest rates have been so low recently that it may be more cost effective for you to get your own loan. You could talk to a Wells Fargo agent who may be able to assess whether her note is truly assumable. If you need the name of a Wells Fargo agent I can provide that for you. Just contact me for the information.
Best of luck to you!