So, Blue we have a predicament with Denise I see. You have not talked directly to her about what you feel based on what she has done? If not this is my first suggestion. To read her mind is impossible and you know that for you know the Bible that tells you that only God can read the hearts and minds of mankind. To speculate is not to yearn for her friendship at any cost. What would Christ Jesus do here? Give her what Christ would have for her to receive from you. You are not your own now you have been bought with a price. Give her the wealth of God's purposes and intentions over your own. This is also my suggestion.
Money may be her motivation - so what! I would then give her some of mine, even though I need it too, as a gift to gain her as a friend, offering it to God as a living sacrifice for His purposes and intentions over my own. God, I would trust, would have my back on my financial needs then as well. I would love on her God's way in other words - not in human reasoning ways. This is absurd to the world in what I mention - but I pray it is not absurd to you being in Christ. I trust I can give you this in love and you will receive it well.
“When I was a child, I spoke and thought and reasoned as a child. But when I grew up I put away childish things,” (2 Corinthians 13:11). One of the “things” includes a selfish attitude. As we grow and mature we realize that everything is not ours and, as a matter of fact, it is all God’s. According to (Psalms 24:1), God owns everything. All the land, all the water, all the buildings, all the cars, all the houses, all the “everything” belongs to God. And He wants us to take care of it all.
Stewardship is taking care of something one does not own. From teaching toddlers to pick up toys to involving preteens in mission projects, we train our children that it’s all God’s and He has given us the privilege to take care of it for Him. Teaching and training children to be responsible stewards begins in the nursery and continues throughout our lives.
As you yield to Christ's vision - this will be an opportunity to be honest with her including the spiritual truths you live in. Do not let prejudice interfere with your godly demeanor and let yourself see the value in (Ephesians 1:18-23) - that at all costs we are to reconcile people to the Lord for the point is in His Saints being a part of His familia; a part of His Kingdom. And eventually a part of the Kingdom of Heaven. Give nothing to grieve the Holy Spirit in, and to rob God of His glory.
Personally - I would find a time to talk openly and calmly about the feelings I had honestly with her and by mention of the specific acts you witnessed. Then I would allow her to speak and I would listen actively and intensely, being quiet within myself. Then I would ask God within myself to open up an opportunity to witness my faith to her in an act of kindness I could give her. Then, as God opened up the opportunity and rendered it clear to my spirit - I would obey Him in doing it.
For instance, when she agreed to give them back, or if she didn't - I would give them to her and a 5$ bill for lunch as well (example). I think of the Good Samaritan story in the Bible, and to this end I see my story allowing my acts to bring glory to God and not securing my rights which I never had in the first place.
"Lord, help in this situation with Blue and Denise, allow Your will to be understood and done Lord. Give Blue Your hand of guidance in this. Bless Denise in ways only You can, and give opportunity for Your message of 'good news' to be heard and experienced thru Blue - In Jesus' name I pray - Amen."