I honestly think you should let them decide. If they are seriously into learning then for starters, their Yeshiva may or probably will give them a scholarship, maybe even full. When they get married, they may or may not be able to make parnussa. Getting a college education is in no way a guarantee, and their are many who have done better without.
If they would like to earn a degree, they could do so on-line, without missing out on sedorim, and going to a physical campus. One of my friends in Yeshiva got an accounting degree through correspondence off hours in Yeshiva, with the Rosh Yeshiva’s knowledge. Probably the only one I know of.
I would suggest have them discuss the predicament with their Mashgiach or some other Talmid Chahcham that hopefully both of you respect. Being supportive is important, and respecting them for their accomplishments.
My feeling is, that it’s a lot easier to work hard and be dedicated to something if it’s important to you. If they don’t see the importance for planning for Parnussah now, they will probably not be dedicated to secular studies, on the other hand if and when they need it for parnussah, they may be far more dedicated.
Good luck!