Yulia Skripal is no longer in a critical condition after she was poisoned with a nerve agent.
Salisbury NHS Foundation Trust said she is improving rapidly and her condition is now stable.
Her father, the former Russian spy Sergei Skripal, remains in a critical but stable condition.
Dr Christine Blanshard, medical director for Salisbury District Hospital, said: Im pleased to be able to report an improvement in the condition of Yulia Skripal.
She has responded well to treatment but continues to receive expert clinical care 24 hours a day.
I want to take this opportunity to once again thank the staff of Salisbury District Hospital for delivering such high quality care to these patients over the last few weeks.
I am very proud both of our front-line staff and all those who support them.
Yulia Skripal and her father were found unconscious on a bench in Salisbury on March 4.
The government says they were poisoned with a military-grade nerve agent and has blamed Russia, expelling diplomats who could be gathering intelligence.
Moscow denies involvement in the attack, which has sparked a diplomatic crisis between Russia and the West.