After all, three times this European season, she has established new personal bests - and take it as read they double as national records - 4.85m at the Prefontaine Classic in Oregon in late May, 4.92m at Mannheim, Germany, on June 23 and 4.94m at Jockgrim, also in Germany, on July 17.
Three times, she's had a crack at the magic 5m mark, although she conceded only two were serious attempts.
"I went to go and do it [at Jockgrim] but wasn't sure," McCartney said this week. "Sometimes you see vaulters will stop when they've done something really big.
"The emotion takes over and it can be dangerous to go and do it again. You're in a whole different place emotionally.
"I started the run and pulled out. All I was thinking was I've just had such a high, such adrenalin, such happiness, and now I'm coming back down slightly and I was worried I would take off badly and injure myself."
One of her major determinations this year was to stay clear of injury after a lengthy Achilles tendon problem caused her issues last year.
She's done vaults when she has known she had plenty of room to spare and had those "I could have done it then" thoughts. But pole vault isn't like, say, long jump, where you leap, make the mark and it's there forever.
"It happens all the time that your best jump is not necessarily when you want it to be. When I jumped 4.92m, I certainly had room to spare and knew I could do the next height but I just couldn't make it work that day."
McCartney has moved to a 14-step run-up and is using 4.6m poles.
"But I do want to work on 4.75m [poles] and I'll be trying to do that after this season. I have to keep pushing my limits and it's quite obvious I need to be on longer poles because I'm gripping it right at the top," she laughed.
Lengthening her run-up and poles offers a risk and reward scenario but McCartney said the extra speed she can get off the 14-step run-up is significant. If she's to scale fresh heights, that is important.
She keeps a casual eye on what equipment her top rivals are using but "it's more curiosity because every vaulter is so different".
"It's a waste of time analysing other people's vaults because you're not that person and poles are very particular to each athlete."
McCartney has four events to wrap up her year. After Birmingham, she will compete at a low-key event in Beckum, Germany, on August 26, the Diamond League final at Zurich on August 30 and finally the Continental Cup teams event in Ostrava in the Czech Republic, where she will represent Asia-Oceania.
McCartney admitted she is relaxed about what lies ahead, figuring she's had such a memorable year, there's no nerves to speak of.
She can pinpoint key moments in her career. Recent events are right up there. She does occasionally stop and think of her progress in the past two years.
Her first 4.80m vault was at Dunedin in the national championships early in 2016. She still rates it one of her best efforts.
"That was an incredibly pivotal year for me. It did show I'm capable of being there.
"Three years ago, jumping 4.80m was such a big deal. The season before I did it, my personal best was 4.45m. In the last couple of years, I feel I've made that next step. That's why I'm so happy with how this season has gone."
It's not as though the 21-year-old spends all her waking hours thinking of 5m as if it is a mantra but her target is clear.
"It's sitting there waiting to be cleared. You can't help but feel the barrier and it can take a bit to get over it."
On one point, McCartney is adamant: she won't stop learning. The longer run-up is a case in point.
"It's good to know I need to keep going, push myself. I'm still learning how I approach things. You can't stop and get comfortable."
All-time top women
● 5.06m: Yelena Isinbayeva (Russia) Zurich, 2009
● 5.00m: Sandi Morris (United States), Brussels, 2016
● 4.94m: Eliza McCartney (New Zealand) Jockgrim, 2018
Also:
● 5.03m Jenn Suhr (United States) Brockport, US 2003 (best indoors)