Hi OwlReally.
If she's a friend then when the dust settles & both of you are no longer angry, then you need to sit down together to talk this through. You need a restorative meeting with her where both you & her can say to each other what it is you are really feeling. If you have been beasties for 15 years, then you must have something. That's not just going to disappear over night! Give yourselves time to cool off & arrange to meet somewhere neutral.
good luck & if the friendship is worth saving, then save it! Xxx