Was there any sort of disagreement that may have led to this either b/w the two of you or her parent(s)? When did you notice the start of her behavior?
Thank you for clarifying.
From what you've shared, she sounds "spoiled" and enabled by her parents to act this way. You've also tried to reach out to her and she's not reciprocating. There are few things that you can do because, ultimately she is the one to decide how to respond.
Speak to her parents about her behavior in a way where they'd encourage her to be respectful and interacting. If she or they feel criticized, they'd either remain passive or turn it somehow onto you.
You may think about not being as generous towards her because she most likely is 1/ expecting that and 2/ taking it for granted. That does not mean that you'd stop being nice and loving towards her. Continue to phone or write/email to her and if possible, arrange for a lunch together either with her parents and her or just the two of you. You may let her know that there is something on your mind that you want to discuss (don't let her know what ahead of time) If she ends up meeting with you alone, after you've had some nice meals, mention to her that you really appreciate when you hear from her and that you're there for her because you love/care. If you express criticism, she may recoil. Rather, keep it on a positive note so she can feel empowered and understand the impact that she has on others.
Try to re frame what you may have been used to saying in the past ex: "its always her way". You're correct, it is her way because she would do what suites her. Yet, you want to reward positive behavior not condone negative one. Find at least 1-2 positive traits of hers to praise and compliment her on, show interest in her schooling/dating life, etc. You could make a picture album with pictures of the two of you from her childhood till the present time and include a card/note about how much you cherish her.
And, as hard as it is, try not to personalize her behavior. At this age, she's mostly egocentric and preoccupied with things that she finds more exciting. Her behavior may not necessarily be 100% volitional intent to hurt or reject you.
Yes, you do have to be more conservative w/ the giving of material things to her. Her parents should not condone her behavior. Maybe they don't see it as a big deal? People should be appreciative when others give them something I agree. In some cases (I'm not saying this is the case w/ her), individuals may become resentful towards the giver because they feel inadequate. Your love can be expressed in different ways than giving, giving and giving. She has to lover you for who you are not what you can give her.