Yes it's normal during pregnancy, but if you keep that way, soon she hardly to walk n cant even put her feet on the floor.
I had this started as early as 18weeks.. hehe!
When she lay down, put pillow under her leg. drink more water (so that she can flush out more) n avoid salty stuff. Wear socks,
she can also have foot spa, can DIY.. put warm water (not hot ah) in pail for relaxing.
My hub did massage my feet like 2-3times a week.
Some said not to walk too much too.. Not sure if this true, cause I heard when nearer to labour, it's good to walk and exercise cause it helps our cervix muscle and faster opening for labour..