it's hard to get plants without snails... that part is true. there are ways around that, but none are 100% foolproof as either the eggs aren't affected or too much can damage the plant and you're limited to what you can do.
however... it's pretty unlikely that the snails were their problem. typically your aquatic snails are going to be your cleanup crew and only eat dead or already dieing plant material. chances are their water and/or tank were not ideal for the plants they chose (or any plants for that matter) in the first place and they didn't know what to do to fix the situation. it's not that uncommon, actually. planted tanks are tough if you don't have the right info and resources. once you know what to do and where to go, it's easy peesy, baby.
expensive is relative as well. there are options and many of them are actually cheaper than what most folks would pay to have a tank without plants. for example; organic potting soil and play sand combined is much cheaper per volume than aquarium gravel from your LFS and it's a great substrate mix for rooted plants.
what your friend was experiencing sounds like issues at the root level. maybe her plants were planted too deep. maybe they were grown emergent and were transitioning, but when she saw all the leafs rot and float away she gave up or dug them out and threw them away. maybe she used inert soil with crypts, swords or vals and didn't have excess nutrients in the water column/didn't root feed/etc. and the results she got were inevitable since she didn't know. hard to say for sure, really without being there, testing, seeing, etc..