What you will need:
Aquarium heater (I had one stowed away with some old aquarium supplies)
Short length of 4" PVC pipe
Pipe flange for pipe 4"
(this can work with 3" pipe as well if you can find a flange that size)
Hacksaw (or something else to cut pvc)
Step 1: First Things First
2. Find an aquarium heater - if you find one with a variable setting, that will make life easy for you. If you buy one with a set temperature, make sure you get one for a small fish bowl. If not, you will need to make your lotion warmer pretty large to keep it from getting too hot.
Do these first because that will allow you to determine the length of pvc.
The lotion bottle I bought was 7 3/4" tall (measure from the top of the bottle, not the top of the pump) and the aquarium heater was a similar lenght. I cut a length of pvc 8 5/8" tall and that allowed the bottle of lotion to not touch the bottom of the flange when it is assembled.
I created an outline drawing in Paint so you can see what I am talking about.
Step 2: Cut Your Pipe
I did not want to buy 10 ft of pvc pipe, so I bought a precut section at Home Depot (warning - the precut pieces aren't that much cheaper than a 10 ft section, so if you have other projects, you may want to go ahead and buy a longer piece).
Step 3: Join the Pipe and the Flange
The picture represents what you should not buy - this is a toilet flange - you need to get one with a solid center (you need to keep the water in...).
After you fit them together, paint them (I painted mine black because I had a can of spray paint laying around).
I used Gorilla to put my pipe pieces together because I didn't have any pvc cement - and mine works fine.
Once again - put them together and make sure it isn't top heavy and after you glue them together make sure they don't leak.
Step 4: Trace / Cut Lid
I then removed the pump part of the lotion bottle and glued the bottle to the lid. That way the bottle would stay suspended above the bottom of the tank and when I pump the lotion, it would not fall into the pipe.
Step 5: Insert Lotion Bottle Pump and Heater
It does not have to be glued together and it does not have to be completely flush to work - but if you ever bump into it and knock it over, the more flush your parts join together, the less mess you have to clean up.
Step 6: Fill With Water, Test and Enjoy
I added a timer later on that way it would be warmed up by the time she was finished getting ready in the morning.
NOTE: I suspended the lotion in water and heated the water because the water temp will max out at the boiling point of water (I learned this from making candles). Lotion has the potential to get hotter than than and can cause burns if you don't know what you are doing. So please don't dump an aquarium heater directly into lotion - that has bad idea written all over it.