England A bowled Australia out for 284 in the first innings of their three-day, red-ball warm-up match in Leicester last week then piled on 562 in reply, led by centuries to Lauren Winfield-Hill and Paige Scholfield.
"It was perfect prep for us," McGrath said at Trent Bridge, two days out from the Test which will begin the multi-format series. "We really enjoyed it. We got tested, we had a long day in the field and we had some really good moments and some moments that we've had some really good discussions about and reflected on. From a preparation point of view, we couldn't be happier. We've had some really good chats, reflected and we're going into this five-day game really confident."
McGrath is vice-captain for Alyssa Healy, who in turn will lead the side in place of regular skipper Meg Lanning, who was ruled out of the tour for medical reasons. McGrath said she was impressed with how Australia had adapted in the circumstances.
"Meg's an outstanding captain and it's obviously going to be a bit different without her, but everyone's stepped up and just found that five percent extra," she said. "It's a collective approach with the side and Midge [Healy] is doing an outstanding job with leading from the front. Every time she speaks, everyone stops and listens. So we're finding everyone's stepping up and doing that little bit extra and we're travelling really well as a group."
Litchfield scored 68 during a 167-run stand with Annabel Sutherland, who made 116, as Australia reached 371 for 7 in the second innings of the warm-up game.
"Phoebs has been unreal," McGrath said. "If I was her, I'd be quite nervous, my first major tour away, and she's like she's been doing it for years.
"She's absolutely killing it, extremely hard working at training, and she's so hard on herself, she just wants perfection. I'm really enjoying watching her journey and I'm excited for her, if she gets the opportunity, to watch her go out there and do her thing.
"I look at our squad and I'm just excited about how much talent there is. You look at the Phoebe Litchfields, the Darcie Browns, yes, they're young in age but wow, they're serious cricketers. I don't think it matters who we put on the park, it's going to be a really good team and yeah, we're missing a bit of experience but we've got some talent and we've got a lot of domestic experience behind us as well so I'm excited for different individuals to stand up at different times."
England enjoyed the best of the weather on Tuesday and were able to train on the outfield at Trent Bridge while Australia had been forced to train entirely indoors due to heavy morning showers. But McGrath didn't believe that would dent Australia's hopes of taking four points from winning the Test, which looks set to be played in finer conditions and with a fifth day providing an added buffer against a draw.
"That's one thing we were really excited about, the prospect of a result, and both teams play a really aggressive brand of cricket and are both in some really good form at the moment," she said. "Personally, I love the five days I'd love to see it from now on. That's where I stand on it. But we'll leave that for others to decide."
If any moisture remains in the air, McGrath will look forward to the chance to try and swing the red Dukes ball, which she said had provided a learning experience in terms of how to use it, but a welcome one ahead of just her fourth Test appearance in what will be 53 matches for her country.
"I'm feeling really good," she added. "If you'd asked me a couple of months ago, maybe a different story when I was learning the red ball. But we've all put in a lot of hard work, we've had a lot of discussions as a team, a lot of discussions with our skill group coaches… everyone's feeling really good about their game.
"We've had a decent training block where we've trained pretty uncomfortable at times and we've come out better for it, so I personally go in full of confidence and I know for a fact that the team goes in really confident as well."
Valkerie Baynes is a general editor, women's cricket, at ESPNcricinfo