I can speak to the experience of traveling to France's Disney park speaking minimal French. I was accompanied by an older child who also didn't speak French at all. We had a blast. Mind, we are rather familiar with WDW, so that was perhaps a significant advantage, but it really wans't very hard to get the gist of most attractions. France's Disney has some things in English, but many things are in French. WDW is much bigger than France's two parks. If your daughter knows many DIsney characters, she'll be well on her way.
Antoher hidden benefit of that trip was that it REALLY motivated my nephew to WANT to learn French (and Italian, but his school only offered French to his age group.) Before that trip, he saw little point in learning a second language, but after he was really motivated. He even learned some words, and got a sense of the sound of both languages.
One disappointment on that trip for him was a castle we saw in Italy in/near Aosta. As Americans, we were encouraged to see the tour at a certain time of day, so we all thought the tour would be in English. My nephew was super excited to see a real castle and to ask questions. He was crestfallen when the whole tour was in Italian, and the tour guide spoke no English. That was really the only time he had a near meltdown. So it can happen. Unlike my nephew, your daughter probably has minimal reading skills, so that may be a small disadvantage.
Even though I don't speak Italian, I do have some basic understanding of Spanish. With just that, I was able to understand much of what the guide said, and quietly give him the gist of the tour. He did end up enjoying it after he got over his disappointment. So disappointments CAN happen, but they weren't our typical experience (to be fair, we did encounter a good number of folks who spoke English.)
Both of us found we were able to pick up on some basic Italian words in just a few days. Young children are especially spongy when it comes to picking up new languages. It will probably help to try and teach her a few basic English words before she goes. It may help also if you are able to find a few familiar sights and/or foods while in WDW. In America, I rarely go to McDonalds, but in Europe, there was something very comforting for both of us about being able to get a Big Mac. It was also great fun to see the menu in a different languages. If you will have a car, including a trip to McDonald's (if your daughter knows McD's) would probably be helpful. (there is on on WDW property, and a huge one up towards Universal Studios) Likewise, I'd consider a dinner at the Italian place in Epcot. You may find it not at all like Italy, but perhaps some menu items will be familiar. At the very least, cast members in that pavillion will all speak Italian.
I do feel the need to relate that a French-speaking Canadian guest recently posted here about her daughter having some difficulties in WDW, but she sort of came off as though she expected cast members to be all be French speakers, which is not the case in America. Many, perhaps most Americans, are truly monolingual. Some Americans can be quite resistant to learning a second language. She kind of got an earful from some DISers. (I'm not taking sides, just reporting)
I say this with some slight hesitation, but although Italian is not very present at WDW, Spanish is fairly prevalent. I know this is an area of some sensativity, and that Italian is NOT the same as Spanish - BUT- as somemone who went to Italy with a rudimentary understanding of Spanish - I found I was able to appreciate the similarities. For that matter, I found my experience with Spanish was even of some help in understanding French. (not so much with German or Polish or Dutch...for German and Dutch, English and linguistics were much more useful.) I imagine that although your daughter is not as strong a reader as I am, her understanding of Italian is probably FAR greater than my mastery of Spanish.
Sadly, America is not nearly so multilingual as Europe (even in it's signage). It should be more multilungual in my opinion. Nevertheless, I do think your daughter will have fun. While some things may be a challenge for her; she may well also come away with a motivation to learn English, as our trip motivated my nephew.
I'd also like to say that Living with the Land has actually always been a well-liked attraction among the children in our family. Maybe they are odd kids, but they get a big kick out of seeing banana trees, giant lemons, and the animatronic lanscape scenes. I also think the slow pace will be helpful in giving you a chance to translate. We even took the backstage gardening tour with two small kids once. It was over an hour long and they loved nearly every minute.
Ooh, one thing the kids like to do on the Land ride is search for hidden Mickeys. That may well also be a fun thing for your daughter to do. All over WDW are Mickey patterns (Two small circles intersecting a large one). They are carved on the backs of chairs, hidden in murals, hiddne in the pattern of your resort bedspread, tucked into metal scroll work, carved into rocks, etc. You don't need to understand English to find them. (there is also hidden Mickey guidebook you can buy.)