There are walk in tubs and showers with very low lips that are commonly available.
However if a shower remodel is not easily available due to finances or loss of bathroom access during remodel, many elders get by in a standard shower by utilizing a shower chair and a handheld shower wand.
A deluxe shower chair - actually a tub transfer bench - extends over the side of the tub, so the elder or disabled person can sit and then slide over into the shower without doing the step over.