Pull the bulb again and check the filaments up close visually to be sure the low beam filament didn't blow again. It could be a short in the wiring that caused the first bulb to blow, and if so, it will keep happening with new bulbs until the short is fixed.
If the bulb has both filaments intact and only one side works on low beam, but they both work on high beam, I'd suspect a wiring or connector issue from the headlight switch to the bulb only on that low beam wire.
Easy way to check is just grab the bulb connector plug when connected to the bulb and with the headlights on low beam and wiggle the connector and the wiring coming out of it to see if that causes the low beam to flicker on. If not, grab the black wiring looms the headlamp wires go into and keep wiggling it along it's path until you reach a point where wiggling the loom causes the low beam to come on.
You should also visually inspect the ground wires/ground points (thin black wires grounded near the rear of the headlamp housings under the hood) for rust or corrosion, and look for another other obvious issues along the wiring path, like a bolt or sharp metal edge having cut into the wiring or loom, or heat having melted the plastic loom and wiring sheath, causing a short to ground.
If its the passenger side bulb that's not working, it'll be a little trickier to get between the radiator and top brace to check that wiring, but you'll want to check all of the connectors, and anywhere the wiring is close to the cooling system or engine.
It may also be the headlight switch itself going bad, which is VERY common with an original switch at this age, but usually that manifests itself as both low beam headlights not working for a period of time, and turning the switch off and then on again can make the headlights come back on. If you don't find any wiring issues, you might pull the switch and check for any fried connectors, or you might want to just replace the switch with a new one anyway if it's never been done. With the switch removed, you can peer back into the dash wiring to see if there are any wiring issues back there, where there are plenty of sharp metal edges to cut into the wiring as well.
