Muir is one of four on the eight-strong British team for the opening World Cup of the season in California to be making their bow as Sam Curry, Joe Evans and Tom Toolis follow suit.
At 20 Toolis is the oldest of the four with Muir, Curry and Evans still in their teens with the quartet joining Heather Fell, Kate French, Katy Burke and Jamie Cooke in earning selection.
And Muir, originally from Dumfries and who trains at the Pentathlon GB High Performance Centre at the University of Bath, admitted the trip to Palm Springs has come as a complete surprise.
"I'm really excited, I thought I'd heard it wrong when I was told," said Muir. "I didn't ever think I'd get to a World Cup this year.
"My aim was to get the junior Europeans and the junior worlds. It will be a really good experience for me and the training in Bath has helped me so much."
The four debutants won't be short of advice should they need it with Fell an Olympic silver medallist from Beijing 2008 and Cooke the 2011 world junior champion.
Fell didn't compete at London 2012 with world champion Mhairi Spence and Sam Murray representing Team GB and the latter following her lead in winning silver.
Cooke also missed out on selection to Nick Woodbridge and Sam Weale while Burke has two fourth-place World Cup finishes to her name and French will contest her third event.
And Pentathlon GB performance director Jan Bartu insists the trip to America is the perfect opportunity to hand Muir, Curry, Evans and Toolis their World Cup debuts.
"It's the first World Cup of the year and it's the right time in the Olympic cycle for these young athletes to go on the international circuit," said Bartu.
"It is in line with our Rio plan, where we wanted to bring new talent on to the world class stage early in the Olympic cycle and see what they can do.
"It doesn't mean that we're not going to consider the more established athletes."