The law has not changed. It is essentially impossible for a UK resident, citizen or otherwise, to bring over a relative other than a minor (under 18) child or spouse.
The lawyer you spoke to advised you correctly. If your sister is not already a graduate, the best option for your sister to come to the UK is to study at a UK university. She would need to pay full international fees, which are very expensive. In this case, she would apply for a Tier 4 visa. After this, assuming the visa system remains broadly the same, she would need to find employment in the UK. The government has announced the reintroduction of the post-study work visa, for students starting this year. COVID-19 has thrown a spanner in the works, and this has not yet been legislated on.
If we assume this scheme is reintroduced, after her degree, she will be able to apply for a 2 year work visa. Following this, she would need to apply for a sponsored work visa. After 5 years on work visas, she would be eligible to apply for settlement, and a year after this, citizenship.
Since her ability to stay beyond the first two years following university depends on finding a sponsored position, she should aim to study a profession which is in high demand. A useful guide for such professions in the shortage occupation list. Aside from being in demand, these professions benefit from some advantages in the visa application process, although these are expected to change with an upcoming modification to the UK's work visa process, and there is also no guarantee that a profession will remain on the list from year to year.