Here are a few options for you to choose from. One might work better for you than the others:
I'd do fewer reps with a heavier weight, maybe at a different tempo from what Cathe does (just go at a pace that feels safe and doable for you).
Or start with a bit heavier weight than you usually use (5-10# more), do as many reps as you can, then change to a lighter weight and finish out the set. Try to get one more rep at the heavier weight each time you do the workout. (This is a 'drop-set' technique). (I personally wouldn't do it the other way around, since you want to be fresh and recovered when you lift the heavier weight, and if you do the lighter weight first, you'll use up energy that could have gone towards lifting the heavy weight, and you won't be able to lift the heavy bar for as many reps as if you start with it. Just make sure you're warmed-up before starting).
Another option is to microload, which is adding very small increments of weight to your bar--barely noticeable. This is often done with .5-1 pound increments, but that's a bit impractical unless you have some of those magnetic weights around. Instead, pick up some 1.25# and 2.5# plates, and start by adding the two 1.25# weights on (to increase your weight by 2.5#), then go to two 2.5# (5# heavier than your current weight), then two 2.5# and two 1.25 pounds (for 7.5# heavier than now), then you'll be ready to go to two 5# weights which you should already have around).
One thing to consider is that if you work your legs often, they may not be getting enough recovery time. Heavy lifting requires more recovery time, so try doing lower body no more than 2x per week while you are building strength.
