I do stupid stuff all the time but seriously? A hood slide? You aren't Jackie Chan or Batman. How large is it in inches? (the dent )
If it is small enough she probably won't notice it but if she does just confess right on the spot. With everyone saying "hit it with a hammer" don't, I did that to a small dent on a beater car that was the same year as your moms Monte Carlo and I ended up putting a surface bulge.