As someone who worked on these models in the consumer credit industry, it is possible they there isn't any discrimination. The only thing that comes to mind is recent inquiries, which have a minimal effect on credit score but are highly predictive of default. If she applied for a few credit cards in the previous half year and DHH did not, it would explain the difference without being discriminatory.

Much more likely, in my view, is that the algorithm looking at something that is so highly correlated with being female (e.g., Homemaker as career) and default. This would almost surely fail existing regulatory tests against discrimination. Since most credit applications ask for household income, ...etc. It is doubtful their applications otherwise looked meaningfully different.

Edit: Checked the application, and you are indeed required to enter in household income and not your individual income if you share a checking account.