Jeep 4WD Question- JEEP GUYS CHIME IN!

This is a question for my friend from work, she has a 2001 Wrangler, and she said that she could not engage 4WD. I checked it out and it did not want to engage past 2H, I checked out online and found they came with locking hubs to engage and disengage 4WD, so might this be the problem why she can’t engage into 4L or 4H? I’m not too keen on Jeeps, or trucks for that matter, so if any of you Jeep guys could help out I’d appreciate it.