I think perhaps that you have not received comments because you have posted on "Other" rather than Design Dilemma.
I've worked with a few contractors and this has not been a problem but all purchases were agreed on between us. Most contractors receive a discount with suppliers and I would get that discount by giving them the contractor's name and job site.
I don't see the problem if you and the contractor agree on the purchase and if you are dealing with their supplier and handing in the receipts other than maybe she is collecting her own points!
That being said I did work with one company that was a husband and wife team for a house flip. She did consults and initial measurements and when it came time for the actual reno there were several glaring mistakes made by not measuring and/or ordering properly. I landed up in between them because apparently she didn't make mistakes. It was resolved to my satisfaction in the end but I would never deal with the company again.
You can talk to your contractor about this but just a warning. Don't get between them.

@boomers775 Thank you for sharing and the advice. I have spoken with the contractor directly and we are agreed on the cc purchases. You are correct about husband/wife teams. It can be a very delicate situation. Luckily, ours worked out and we are all on the same page. Phew!

Good news!