Buy a bag of those Hershey Kisses, my favourite are the caramel ones. Take them out of the bag so they look like more. If you live in the same home, make a trail (or leave a bunch of them together with a romantic note) of Kisses leading into the bathroom where you are waiting to begin filling the tub and have a selection of nice smelling things to add to the bathwater. None of the nice smelling things has to cost much, try shopping at a discount store. Open the caps on the bottles and smell them before you buy. Make sure each is nice, look for vanilla, peach, lime, etc. Natural smells are a pretty safe bet.
If you don’t live in the same place as your Valentine give her the nice smelling bath lotions, potions, shower gels, bubble baths, shampoos, etc (two or three items is enough). Presentation is the key. Go to a Dollar Store and look for the Valentine stuff. Pick out a pretty card, for a buck. Pick out something you can put your present into – a basket is ideal. Or a gift bag, a storage container if it’s not huge and you can find one in a Valentine colour (pink or red, white is ok), do not buy a floor cleaning bucket or anything which is used for housework. Think romance. Add fluff of some kind to fill up space in the basket or whatever you end up with. Not fluff literally, but look at things in the Dollar Store like chocolates, knicknacks, tissue paper (think stocking stuffers but with a Valentine theme).
Have a look at the artificial flowers at the Dollar Store too. Some look quite real and those would be great to go along with your Valentine gift. On the side or as part of the whole presentation, try picking colours you know she likes or stick to the traditional red, pink or yellow for friendship.
More than likely you can do the above for about $20.00.