Hi kansashane,
The amount of give will vary with the firmness that you choose but soft latex has lots of “give” and can be very contouring and as pressure relieving as memory foam. If you have concerns then it may be an idea to test some softer latex mattresses locally so that she has a better sense of what latex can feel like in different firmness levels.
There is more about the many variables that can affect sleeping temperature in post #2 here (including your mattress protector, sheets, and bedding) but it will also depend on your physiology and where you are in the “oven to iceberg” range so it isn’t really possible to predict until you sleep on it. For most people it would be fine but for a few it may be a little warmer than some other types of mattresses and in this case you may need to compensate in other ways (bedding, bedroom temperature, mattress protector, a mattress pad, sheets etc).
While both memory foam and latex can be very pressure relieving in a suitable thickness and firmness level (they both come in a range of firmness levels) … they have a very different “feel” (see post #2 here). Memory foam is also only used in comfort or transition layers and it’s used for pressure relief … not for support. Pressure relief, support, and “feel” are all very different things.
There are too many unknowns, variables, and personal preferences involved for anyone to be able to predict whether any specific mattress will be a good match for someone else in terms of PPP based on specs (either yours or a mattress) or “theory at a distance” and when you can’t test a specific mattress in person … then the the best source of guidance is always a more detailed conversation with a knowledgeable and experienced online manufacturer or retailer who will know more about their own mattresses and how well they are likely to “match” different body types and sleeping positions based on the “averages” of their customers than anyone else and can help “talk you through” the options they have available that would have the best chance of success (see mattress firmness/comfort levels in post #2 here).
If you are buying a king size then the Dreamfoam latex mattresses have a split layering option where each side of the mattress can have a different firmness level that can be customized for each of you that may also be worth considering.
Phoenix