Yes, she is. It sounds harsh for her to say that she loves her father no more and no less than the father-daughter bond, or at least, it sounds harsh compared to her sisters' expansive claims. That sounds like she's saying, "I do what's required of me—no more!" However, if you (and Lear) really understand how deep and profound such a bond is, you can see how deep a love she's promising, and her actions later in the play show that this is the case.

Greg