Your translation got the gist correct.
A better way to approach it, though, might be to focus on -는 것이다 (and related phrases like -ㄴ 것이다, -ㄹ 것이다, etc.) and -ㄹ 수 있다 separately. These two are very widely used grammar constructs, and -ㄹ 수 있는 것이다 is just a particular case of connecting the two together. It makes up a very small fraction of their usage.
In fact, the way it is used in your example doesn't sound the most natural. We are more likely to phrase it slightly differently, like 강건할 수 있을 거예요.
- -는 것이다 is structurally similar to "It is (just) that ..." in English. 것 (a thing, fact, matter, etc) often refers to an abstract idea or fact, creating a noun clause the way "that" does in English. Its usage is a lot more prevalent in Korean though. It basically makes the embedded clause into an entity to be considered with renewed focus, thus creating an effect of objectifying, emphasizing, dramatizing, etc. depending on the particular usage. Often it is very subtle so that the only effect is a minute nuance with no change to the overall meaning.
Note the variations with different tenses.
- -는 것이다 = about what's happening now or an established fact. 시간은 끝없이 진행하는 것이다.
- -ㄹ 것이다 = about what is to come (future or possibilities). 우리가 꼭 승리할 것이다.
- -ㄴ 것이다 = about what's already done, or a certain state. 그 일은 이미 끝난 것이다.
Your example is about someone's health, essentially a possible outcome, so -ㄹ 것이다 would be better even though -는 것이다 not wrong either.
- -ㄹ 수 있다 signifies being able to do something or a certain expected possibility or probability. E.g. 나는 100미터를 13초에 달릴 수 있어요 (I can run 100 meters in 13 seconds), 사고는 언제든지 일어날 수 있다 (An accident could happen anytime). It is the main phrase corresponding to "can/could/might", "is able to", "it is possible (for something to happen)" in English.
Comparing 사고는 언제든지 일어날 수 있다 and 사고는 언제든지 일어날 수 있는 것이다 might help your understanding. The former is a straightforward bare-bones statement, whereas the latter states it a little more like a principle by embedding the idea in -는 것이다. 것 here can be taken to mean a concrete thing, as in "something that can ...", as well as a grammar construct of embedding and referring back to the given clause.