If I'm an adult and a legal resident in the US who was adopted by a US citizen last year, is there any way she can sponsor me to USA for permanent residency?

Your question is somewhat confusing.  If you are a legal resident, why would you need to be sponsored for residency.  The law about when a adopted child may be sponsored is complex and if you were adopted as an adult, you would be ineligible.  If you were adopted as a child, then it depends on when and how the adoption was finalized and the manner in which you entered the country. I would recommend consulting with an immigration attorney to discuss the specific details of your case.