The thrill of the chase may be gone for her after having hooked up with you last weekend.
In so doing, there is no more mystery for her to uncover.
Oftentimes, this can kill excitement in people and lead them to looking elsewhere for new thrills.
Also, the text conversations that you had with her during the course of the week may have made her realize that the both of you wouldn’t be a good match for future hookups or a long-term relationship.
She may not be necessarily looking for a long-term relationship at this time, even though she told you that she was.
She may have only told you that so as to use the easiest or most convenient way to go about ending her interaction with you.
Being that she already knew that you didn’t want to be tied down, she may have figured that you would have easily accepted her reasoning and let her go.
When you came back with letting her know that you were not against a relationship, she told you that she was not feeling the relationship anymore because that was all she could think to say at the time.
She wasn’t expecting you to come back at her with that.
Again, she is probably not even looking for a long-term relationship at this time.
Her real issue is most likely that she is just not turned on anymore and she may feel the need to go elsewhere to get her thrills.