She could no longer run or practise as a midwife, and it compromised how much she could do for husband Simon and their four children.
As Nic struggled to come to terms with this series of losses, she was further diagnosed with hip dysplasia - misalignment in the hip joint. Rather than see this as another blow, the diagnosis ignited her fighting spirit.
"I had been pushing my way through the pain of running with rubbish hips all my life," she says.
"I thought: maybe I can use that same strength of mind to teach myself to walk, and then run again? After all, brain trauma patients are able to function over time - they relearn things like speech and mobility."
Nic had a complete hip replacement, and was given the all-clear by her surgeon to run. She was thrilled.
"I intended to try and get up to running a 5km race, but Kiri Price convinced me to come along to an Achilles training session.
"I hadn't really thought of myself as disabled, or an athlete, so it took some convincing!" Achilles International New Zealand is a registered charity that provides coaching, training and support for disabled athletes to participate in mainstream events.
Peter Loft established Achilles NZ in 1993, after he had trained and accompanied amputee John Riley to the New York City Marathon.
There are active Achilles chapters in Auckland, Rotorua, Wellington and Christchurch, with a chapter currently being developed in Dunedin.
Loft feels one of the barriers to joining Achilles is that disabled people often don't think of themselves as athletes: "When we think of disabled athletes, we usually think about amputees and blind athletes.
"But there are a range of disabilities. More and more we have stroke survivors joining us, and people like Nic with MS; these are the people I want to come to Achilles, those who don't even realise they are athletes."
Fortnightly training sessions are run at each Achilles location, and Loft encourages able-bodied friends and families to come along and offer their time as guides: "Everyone should come to an Achilles training session.
"Once you spend time with us, you stop seeing the disability, and start seeing the person. You see a missing limb - we see an athlete."
Achilles NZ has taken more than 200 athletes to the New York marathon over the past 20 years, and every single athlete has finished.
Loft feels this may be due in part to the team talk he delivers to them on the start line: "Failure is not an option for you today. If you don't finish, you had better be in an ambulance."
Loft is delighted to have the support of Kiri Price from coaching group Get Running, who has recently taken over the Auckland training sessions.
"It has been fabulous having Kiri come on board with Achilles.
"She is doing an amazing job with the athletes - she brings passion, and an ability to build a group."
Over the next year, Achilles teams will be entering the Auckland, Taupo, Wellington, Christchurch and New York City marathons - and Nic Miller-Clendon is delighted to be going too.
"The opportunity to join Achilles and run the New York City Marathon upped the ante for me. I don't have any feeling in my legs. I can't walk straight, but I can run! I just point my chin forwards and fall for however many kilometres!"
Nic and husband Simon regularly attend the fortnightly Achilles training sessions at Millennium Stadium, where Simon acts as a running guide.
Nic laughs: "Myself and one of the blind participants are very competitive. It sounds ridiculous - but we love racing each other; sometimes it can be a bit disconcerting for the new guides who are just learning!"
Achilles athlete training sessions
What: Disabled athlete training sessions
When: Tomorrow (and every second Sunday)
Where: Auckland, Wellington, Christchurch, Rotorua. Dunedin coming soon.
For more information: www.achillesnewzealand.org/training.html
