Britney Spears is looking forward to a fresh start as she returns home from rehab. “She’s doing really well,” an insider told Page Six Thursday. “She’s healthy and happy and feeling very positive and excited to start afresh. Rehab was a great opportunity for her to ground herself.” Britney Spears (seen here) is feeling optimistic following her rehab stay. Britney Spears / Instagram “She’s doing really well,” a source told Page Six about the “Toxic” songstress (seen here) on Thursday. Instagram/@britneyspears We’re told Spears, 44, finished up treatment last night and was “looking forward to a bright future” following her DUI arrest on March 4. Another source told us that she would be “continuing counseling remotely.” The “Toxic” songstress checked herself into rehab for substance abuse on April 12 after she was believed to have been under the influence of a cocktail of alcohol and drugs at the time of her arrest.…