Change of sponsorship for B2 visa


My mother currently holds B2 visa sponsored by my husband who is on H1B. She has already visited the US once in 2016. She is in the US on her second trip for 6 months. Now my brother is also in the US who holds H1B and we would like to change her sponsorship due to some personal issues. Can anyone give an insight on the procedure to change the sponsorship while the person is in the US?

Thank you.