I think just explain to DD beforehand and show a couple of pictures. Then it shouldn't be a problem.
When DS2 was 5, one of his classmates got leukemia and had to wear hats, tubes and so on, so a special nurse went into the school to explain to his class what they were all for, with a teddy for demonstration.
The kids were absolutely fine about it and weren't traumatised at all, because they had an idea what was going on and the need for 'strong medicine' in such cases. In fact DS2 became very good at taking medicine when necessary, because his attitude was that his friend's medicine had to be worse than his, so the least he could do was to take his without protest.
Kids are very resilient about such things.