Im not entirely sure what gravimetric methods are?
Precipitate, filter and weight. In case of calcium you precipitate oxalate and weight it after drying as oxalate, or - after roasting - as CaO.
When I asked my teacher what I should do for my second method, she said that i could do another titration with another chelating agent which complexes with calcium?Im just not entirely sure what other chelating agents complex with calcium other than EDTA.
Most of them. For details you have to look into textbooks (or start checking which reagents are in the lab, that should give you an idea which method can be used). My textbooks are in Polish, so they will be of no help to you
What I don't like in this approach is that basically you are doing second almost identical determination, as all complexometric titrations are similar, regardless of chelating agent used.