Hi Andy,
You have this CSS code on your site.
.nav-aligned-right .main-navigation ul {
display: flex;
flex-direction: row-reverse;
align-items: center;
}
flex-direction: row-reverse;
makes the flexbox contents display in a row in reverse order.
You can try adding this code:
ul#menu-primary-marketer {
flex-direction: column;
}
This specifically targets your sliding menu to display in a vertically stacked manner without affecting other ul navigation elements.