First, I think you're nuts for tinkering with such outside Japan, even if you're Japanese. And she was Japanese. I take it both are not.
Naninani-chan is an affectionate diminutive typically used to address young females. I grew up in the American South - I liken it to 'Sarah, sweetie, go get uncle NBK a cold one.' 'Thank you, honey....' POP。。。。。Appropriate when appropriate, but not something you want to get wrong.
In my experience, in Japan 'chan' it's used with female children and young ladies in an inclusive manner, as in, if one of our judo association instructors looks around and yells, 'Atsuko chan, get over here!', she's probably one of his group or an extended group and personally familiar to him.
'Kun' is used for familiar, in-group inferior (in age / status) male. Standing in front of the Suzuki family, a judo instructor says 'Suzuki kun done good today', everyone knows he's talking about Young Master Suzuki, the boy. The father might be addressed as 'Oto-san', Honorable Father, Suzuki san if personally known, etc.
In my research of Kano shihan's life, I find articles where some Diet member or politician cites Kano shihan as 'Kano kun', even though Kano shihan was elderly at the time, and senior in many cases. In this instance its use is a sign of collegial familiarity and affection, as in 'My Dear Colleague Kano'. But if addressing the President of the House of Peers, the same person would say in general 'His Excellency Konoe', by position 'President Konoe', or Imperial title 'Prince Konoe'. If the same person were to say 'Konoe kun' you would know that their personal relationship predated the Prince's elevation to the higher status position, and the discussion is a friendly one. Conversely, the same person later talking about 'His Excellency President Prince Konoe' in a quote might mean disapproval, hence an intentional distancing and increased formality. (As in when one guy in particular in my judo association switches from 'ランス kun' to 'Gatling san!' I know I've screwed something up, and he's about to address that in a semi-formal manner. Time to pay attention, he's serious, and wants me to know it. It's hardwired in his culture.)
In Japanese business, at least 30 years ago when I started here, it was normal for senior, male Japanese managers to use the first name of female employees close to them as FIRST NAME chan to address them, as in 'Kumiko chan, please bring NBK and me a couple of cold ones.....' I took and do take it as a sign of normal, traditional Japanese patrimonial culture, but was never comfortable doing it. And was right not to do so - as I would not ever take on all the responsibilities that relationship implied, which in the event of young professional women could even mean helping find them a husband, acting as a go between, guarding and guiding their careers, etc.
I would and do always err on the side of courtesy and caution, and would say, 'Koyama san, thanks for the cold beer....' My way of saying 'this is a straight business relationship, don't expect me to help you find a husband'.
And by the way, these addresses often extend for the life - I see 80 year old men addressing 60 year olds as 'kun', sometimes implying their relationship extends back decades or even a lifetime. But it could also be that the young 'un is a recent member of the local gateball association, and is being identified as the junior in the relationship.
So, in short, she's not right.