There are no known interactions between Valerian and albuterol inhalers. Most of Valerian’s potential interactions occur with other prescription sedatives. However, if you want to be safe, start the supplementation with Valerian at a very low dose. A normal dose for the average 4 year old would be 30 drops 1-2x daily. You might start with half of that dose to see if there are any negative effects.
In most individuals Valerian is used as a mild calming or sedative agent. In rare cases it can be mildly stimulating. Albuterol is also stimulating so you might see a slight worsening if you child is among the 1% of people that react to Valerian with stimulation. Currently, there is no significant literature to suggest that using Valerian in your situation would pose any major risks to your child.