Set the Table
That holds all things
The Periodic Table of Elements
Find the two most important places
To the right of the bottom one
Wasn't really sure what this means specifically, but combined with the password hint and the logic of the next line, I made an assumption and went with it. It may have something to do with which version is being referenced.
Take the first three letters. Keep the capitalization intact. Now add the first two letters of her first name. Capitalization intact.
The only thing that makes sense here (and just so happens to fit the hint) is Curium (Cm), named after Pierre and Marie. So, we get CurMa. "r" is the 3rd letter, and we have an "a", so there are probably only 4 characters after this.
Take away 49. Add the symbol. All caps.
Chemical number of Cm is 96. Take away 49, and you have 47, the chemical number for Silver (Ag) -> All caps -> AG. We have CurMaAG.
Add two and take the square root. Use the other number of it rounded to the nearest whole number. Now place the number between the doubled letters.
Add two to 47 yields 49, and taking the square root yields 7. Nitrogen (N) has atomic number 7. The "other number for it" might refer to the Standard atomic weight of Nitrogen, which is 14.007. Rounded to the nearest whole number yields 14. Place between the doubled letters, and we get CurMa14AG. Voila!