Trail Conditions in Highline Canal Trail in Denver

I have a female friend looking to buy an inexpensive bike for casual use. She's right by the highline canal trail, will not often be on roads, and isn't highly experienced. She says it's a gravel trail, she's riding it on a cruiser now but she says sometimes it feels like the front wheel sinks or sticks. I'm trying to decide between a hybrid or a simple hard tail mountain bike. Thoughts?