It was $20 pp with champagne and $10 without. You would have to check once OB to see if and when it will be offered. They usually have it on longer cruises, not sure about the 7 day, if that’s yours.
It is a white glove service, with fancier pastries and sandwiches. It usually is held in the center of the piazza (circle), if the ship has one. Sometimes it could be held in a different venue.
Tbh, I’d just do the free afternoon tea in the MDR, on sea days, as there is already a huge amount of food and very nice. She would probably love it. Most of the MDR teatime’s they wear white gloves also, except once, that I recall.
We usually do tea time on our balcony or room because it’s an elite benefit we enjoy.