OK I am invested in your holiday now!
I still think Florida is risky weather-wise but you might be able to do it relatively cheaply.
Flights x 3 mid-week inc 1 checked case (food on way out, souvenirs on way home) about £1500
14 nights in a small apartment with a tiny kitchen (but it probably won’t have an electric kettle) mid way between Disney and Universal https://www.booking.com/Share-ryIs9F about £1k
It has a free shuttle to the parks. You can work out Uber costs to the Florida Mall etc. for Hot Topic. (Shopping is no longer cheap because of the poor exchange rate so your DD may be disappointed).
Park tickets - you can get 14 days Disney (parks and water parks) for £550 ish each and 1 day for £130 ish each. Going on a coach trip to Kennedy Space Centre will cost you another £130ish each, ditto a Universal day, so you can see how it adds up and how much better value the multi day tickets are. So, somewhere between £2000 and £800 for the three of you depending on how many/which park days you want to do. Ditching Disney and just doing Universal is a slightly cheaper option.
So total so far somewhere between £3300 and £4500.
You can eat counter service fast food to avoid tipping - in the parks and outside - as well as supermarket food. The only other thing is airport transfers and Ubers.
The DIBB boards used to have long running threads on doing it all on a shoestring, so if you’ve been bitten by the Orlando bug (and goodness knows I’ve been there…) pop over there to get tips!