A shower inside the trailer adds weight
. Hot water tank plus its 25 - 48 pounds of water in it, and it uses a lot of space. Making you second bed a problem.
So maybe think outside the camper "box".
There are tall phone booth sized tents with loose weave floor that drains, many people set those up to use as a shower. This would move the shower outside. Some of these are specifically designed for use as a shower stall.
Many options exist for portable showers. Ranging from 2 liter soft drink bottle(s) with small holes drilled in the cap, left out in the sun to warm at the low end all the way to portable propane
powered water heaters with 12 volt pumps.
Depending on your daughters age a small tent outside the camper could provide a place for a bed allowing for a shower inside a smaller campers closer to your weight
range. In a pinch your daughter could use the pad and sleeping bag from the tent right on the floor, provided she fits in that space. Crowded but if one arrives at campground in the rain and wants to avoid setting up tent until weather clears....
It has been noted by many in reviews that these "shower" tents can not generally support the weight of solar
shower bags commonly sold as camping equipment being hung from the ceiling.
Have to ask yourself how much use will you make of the sleeping accommodations for daughter vs. how much use will you make of the shower. And your comfort level with using a rustic solution.