The feedback offered may not be what you want to hear.
Even though you have showered her with gifts and attention/affection, in order for the relationship to survive and continue, the feelings must be mutual.
There is also the age difference. She may have taken advantage of you at one point or had a different idea from the start what she wanted from you or the relationship. It sounds like you are not interested in a platonic relationship with her.
It is possible that once your wife had died, you had found some comfort with this woman and displaced your feelings onto her. You may have to engage in some self introspection as to whether or not this is love, lust or just a distraction from reality.
If she is straight forward with you in regard to what she wants, then let it be. If she is giving you mixed signals, confront her.