Unlikely? There is no standard math requirement for music majors, and that's pretty well known.
> Would we be having this conversation if she had no degree? (Of course not.)
Yes, even more so! A chief security officer with no degree presiding over the security of a nation's credit data?! I mean, she's already under scrutiny because Equifax has been hit by three big stories in the past couple weeks demonstrating their absolute lack of concern for security: the breach, the "random pins", the admin/admin credentials.
"A chief security officer with 15 years of experience and peer accolades in the fields of banking-grade security and human data management"
Typically, this is where most people don't even ask what a degree is. However, as you indicate "no degree" is unacceptable: Which domain-relevant degree programs, initiated 20+ years ago and completed 15 years ago, would satisfy your terms?
You imply that Music is a non-technical degree, which is arguable, but it's certainly an Arts degree rather than a Science degree. If that's the distinction by which you draw the line, you're wrong to do so. If you reject job applicants to a technical role on that basis someday, that's more overlooked high-value opportunities for others to hire instead :)
The odds are near zero. Everyone learns their own domain. Quoting random properties of a specific subdomain of a branch of all possible learning demonstrates your knowledge, not disproves theirs.
And, then, given that Music is entirely dependent on mathematical principles, and Music Theory especially: What are the chances that, as an MFA in Music, she has a rock solid background in mathematics?
Does that make her choice of degree less distasteful?
Would we be having this conversation if she had no degree? (Of course not.)