Here are a few factors to consider before you throw good money after bad adapting a ground tent to an elevated platform.
Wind; this force of nature will kill your dreams. Purpose-built RTTs have rigid pole frames, a captured base, and heavier fabric that handles the wind with greater ease. Your average consumer grade family ground tents get pushed around by the wind pretty bad, elevate them 4-7 feet off the ground and hold onto your hat. I we were talking about sturdy alpine ground tents like a TNF VE25 or a Mountain Tent or a beefy canvas wall tent like a Kodiak I wouldn't as concerned about the tent folding up on you. The captured based of a RTT keeps the wind flowing over the tent or under the rigid base, not between the base and tent floor. This isn't nearly the issue when the tent is pitched in the grass, but it does play a factor when you find yourself pitching one at elevation on a rocky bluff. You are essentially recreating the latter by mounting a tent to an elevated platform. To combat this you would have to modify your ground tent by adding additional stake out loops.
I definitely understand the desire to stand up in your tent, but that adds new requirements to your trailer setup. Crawling around or even sitting up right in your tent distributes the weight around and makes additional stabilization not as great of an issue. Unless you have a great deal of weight over your trailer's tongue, you might find yourself tipping the trailer when you are standing aft of the axle (you may weigh less, but you are are applying greater torque relative to the axle when elevated and standing). Sandbags on the tongue and/or rear stabilizers could solve this. If for some reason you stumble or fall into a tent wall (drunk, not as level as you thought, soft ground or trailer suspension, pant leg not quite cooperating while getting dressed, etc...) the tent won't be rigid enough to prevent disaster. On the ground this isn't a big deal, elevated it will be painful and will more than likely render your tent unusable.
Not knowing how old your daughter is, a RTT with an annex below would give you some privacy from each other by having her sleep down below. Now that my daughter is in her teens the desire for privacy is mutual. I have found that the inability to stand up inside my RTT isn't the factor I thought it would be since I can just climb down the ladder and get dressed below in the annex. With a giant M101 I don't see the need to store any gear in your tent so you may find your tent overly spacious (good in summer, bad in winter). I even have room to put a Luggable-Loo toilet in the annex in addition to my daughter's twin air mattress and "nightstand"/crate that I put my Buddy heater on in the winter.
If doing it for the sake of being able to say you did it is important to you, then by all means go for it. IMHO the cons outweigh the pros on this project. I think that you'll find that the convenience and money saved will be much less than you imagined at the outset. Until I owned a RTT I didn't understand why what you are proposing wasn't the way to go. Sure they could be cheaper, but the design choices and compromises make sense once you spend a weekend in one. Put money aside for a while and just get a RTT (Tepui even makes a massive Gran Sabana if the space is that important) when you feel comfortable dropping that kind of money on one. At the end of the day, it is just a luxury of convenience item for us in the US. We simply don't have the predators here that make elevated sleeping a lifesaving necessity.