My 7yrs old daughter had asthma and coughing tonite she is using steam vicks with water.but my 6months baby sleeping with her..is that ok for my baby?

Yes, if just asthma : If she just has asthma and no fever or any symptoms of a viral or bacterial infection it is then ok.

Maybe,maybe not: I have never been fond of the "vapor" stink as treatment for anything. I find the idea that stinking up the room with a noticeable fume is more likely to aggravate a cough than help it at any age. There are some decongestant effects, but the irritant value is similar to paint fumes.

Asthma: If your 7 year old has asthma and is coughing i would want to make sure you are treating her asthma with her asthma medication not just steam vicks. If your 7 year old has asthma triggered by a virus(common cold) then keeping her in the same room as the 6 month old will put the baby at risk of catching the cold that triggered the 7 year old's asthma.