English is pretty open to the creation of new compound words, especially when using recognised suffixes or prefixes.
The suffix 'struck' literally means that you have been struck by (in the sense of having a sudden feeling) whatever it is suffixing. For example, "dumbstruck" means that you have been 'struck dumb', or suddenly unable to speak; and "awestruck" literally means that you have been struck by, or suddenly overcome with awe
However, many words with this suffix have idiomatic, figurative uses. For example, 'thunderstruck' means 'surprised', and 'starstruck' means that you have been overawed by someone's degree of fame.
From the context of your example, where someone responds with "silence" and then someone else volunteers to speak instead of them, I think the intended meaning of 'wordstruck' is suddenly unable to find words with which to respond, perhaps due to a sudden feeling of nervousness.