"It's a giant move for me," she added.

After working for Phelps Dunbar in Houston, Hall helped launch the insurance coverage boutique now known as Hall Maines Lugrin in 2000. (The Hall in the 17-lawyer firm's name is her husband, shareholder Clifton Hall.)

Wendy Hall went on a leave in 2012 for some surgery, and was ready to return last year, but that did not work out, so she reached out to Joseph Ziemianski, a friend who was a co-chair of Cozen O'Connor's global insurance department, who told her he had been looking for a lawyer with her specific expertise in the energy sector.

Ziemianski could not immediately be reached for comment, but in a statement in the firm's announcement, he said Hall's "knowledge, depth and experience in the energy sector will provide our domestic and international clients with an outstanding resource to handle the most complex cases."

Hall handles insurance litigation and policy issues in the oil and gas sector, representing insurance companies, Lloyd's Underwriting Syndicates, London Companies, and companies in the energy sector. She works in the U.S. and internationally, especially in London.

Because she has been away from the practice for several years, Hall said she did not bring clients with her, but she anticipates helping Cozen O'Connor build its coverage practice in the oil and gas sector. She said she looks forward to working at a full-service firm with an office in London, where many insurance companies have operations.

"Cozen has truly welcomed me with open arms," Hall said. "[In] the insurance coverage oil and gas energy sector, there aren't a ton of us. It's pretty specific. They are happy and I am happy and we are all happy on it together."