Anagram - string.Remove function - good idea

Anagram7.cs

using System;
using System.Collections.Generic;
using System.IO;
class Solution {
    static void Main(String[] args) {
        int T = Convert.ToInt32(Console.ReadLine());
        string[] lines = new string[T];
        for (int i = 0; i < T; i++)
        {
            lines[i] = Console.ReadLine();
        }
        for (int i = 0; i < T; i++)
        {
            if (lines[i].Length % 2 == 1) Console.WriteLine("-1");
            else
            {
                string s1 = lines[i].Substring(0, lines[i].Length / 2);
                string s2 = lines[i].Substring(lines[i].Length / 2);
                int diff = 0;
                for (int j = 0; j < s1.Length; j++)
                {
                    if (s2.Contains(s1[j].ToString()))
                    {
                        s2 = s2.Remove(s2.IndexOf(s1[j]), 1);
                    }
                    else diff++;
                }
                Console.WriteLine(diff);
            }
        }
    }
}