In most cases, setups like this are written as joint ownership. Which basically means your mom owns half, and her sister owns half. When her sister passed away, her will would determine who inherited the property (and any debt that might come with it). Assuming her daughter is the legal heir to the property, then yes, she may be able to force the sale of the house to get her half.
Generally, only couples are allowed to use the joint right of survivorship deed designation, which would have given your mother the entire property at her sister’s death.
The other option is your mother could buy her out. If that happens, then she would gain full ownership.
Having said that, this is a legal matter that requires a local attorney who knows the law in the county in question. The above answer is generally true. But each state has different laws, so it’s critical to seek professional advice before making any decisions.
Good luck