My wife has given a valium 10mg to her mother she has never taken it to help her sleep she has asthma and is sick with a chest infection will she be ok?

Would keep a close eye on her. She should be ok but would not give her valium anymore unless under a doctor's direction. It can impact her breathing if she has underlying breathing issues.

Would suggest caution and getting your mother in law physician involved in case a sleeping aid is needed. Benzodiazepines, such as diazepam are to be avoided as much as possible due to their significant side effects profile, specifically in the elderly.