AITA for expecting roommate to split costs of housewarming party?

My roommate (29F) and I (26F) decided to throw a housewarming party in our apartment this weekend. A few days ago I told her I was thinking it would be good to put in a bulk order for stuff like paper plates, cups, napkins, pizza, maybe some chips and sodas, and she got upset. She said that providing food was my idea when I sent out the partiful. After some back and forth she said she would chip in but I needed to run it by her first.

We might have had different expectations of what hosting means (for me, hosting means providing food and basic supplies) but I was always under the impression we were joint co hosts. It was originally my idea but she agreed and invited her own guests as well. Before I sent out the invite, I wrote up a quick blurb, and sent it to her asking if it was okay/for approval. The invite said food would be provided but to BYOD. If she had a problem with chipping in for food I would have been fine with taking it out but she okayed the invite. Maybe she assumed because it was "my idea" to include that part I would pay for everything??

As a note, I didn’t actually order anything yet, and was planning to discuss with her what to order before actually doing so, since buying whatever I wanted and just hitting her with a bill afterward would be an A-hole move. But she’s upset at being asked to pay for anything at all.

I guess I didn’t really think it was necessary to be extremely explicit up front about splitting costs or labor and the fact that we are hosting together implied we would split everything together. Like in the same way that I didn’t feel like it was necessary to check if she would help with cleaning up or setting up.