When Nana isn't working, she enjoys art, skiing and playing her guitar. She also enjoys visiting antique shops looking for hidden treasures and is looking forward to exploring Taranaki as she settles in to her new home.
Mary Anne says the practice has grown considerably since she first purchased it over 35 years ago and the time is right to bring in a second dentist to the team.
"When I first purchased the practice from Dr Kerry Hamilton and Dr David Haszard it was only open one day a week. As the practice grew, that changed to four days a week and then once the other dental practice in Stratford closed about 15 years ago we have got even busier."
As well as growing the general practice, Mary Anne has developed a strong interest in paediatric dentistry over the years, gaining additional qualifications in the field and now seeing many young patients from all over Taranaki and Whanganui.
Taking on Nana means the busy practice can continue to serve patients of all ages as well as enabling Mary Anne to continue to meet the needs of her younger patients as well.
Mary Anne says since she first gained her diploma in paediatric dentistry from Otago in 1996, the need for specialist dental care for young children has increased greatly.
"I see many children aged six or under who need to come to a paediatric dentist because of the large amount of decay they may already have in their teeth, or because of anxiety they have regarding a dentist visit."
Children are more anxious nowadays she says, so having a special area where children can feel relaxed is important, as is being able to take extra time with her young patients to reassure them throughout.
While Mary Anne knew the practice had room to grow, she hadn't actually got as far as actively seeking a new dentist when she met with Nana.
It was at the suggestion of a mutual friend that Mary Anne Costello and Nana met, and the two dentists soon recognised they could work well together, says Mary Anne.
"She and I will make a good team, and I know she will be made to feel very welcome in Stratford."