The text makes it clear that Elli comes and visits the Jews who are hidden often and eats with them, and then does her best to try and get them things that they need from the "outside" where they are unable to go any more. For example, Anne Frank reports how Mrs. Van Daan says to her,"Oh, Elli, I have only one little wish..." and how Elli responds to this by winking at Anne. She also warns the Jews if there is any danger of discovery through the sounds they make. In fact, if we examine the text carefully, we can see that Elli tries to be so helpful that she actually makes herself very stressed, as the following quote establishes:
Elli had a fit of nerves this week, she had been sent out so often, time and again she had been asked to go and fetch something quickly, which meant yet another errand or made her feel that she had done something wrong. If you just think that she still has to finish her office work downstairs, that Koophus is ill, Miep at home with a cold and that she herself has a sprained ankle, love worries, and a grumbling father, then it's no wonder she's at her wit's end.
This gives ample evidence of the way that Elli served the Jews and did her best to identify with them and their state. Let us remember that to hide Jews or to aid them in any way was a crime that many people were sent to concentration camps for committing, and so Elli was endangering her life by helping the Jews.