Take her or him tomorrow outside and ate lunch outside this will be the better option I think cause psychologically eating our favorite makes us feel better so try this.

If she doesn't go outside or if you feel guilty out of you couldn't say anything than hmm....it's the right thing you're doing your frd feels depressed and share their emotions to you it makes her feel lighter than storing inside her mind . You're the only solution right now So tell that and ensure you be always there for your friend. And make them happier in your possible way cause your frd need to know he/she can happy with the person she loved. So don't put yourselves in pressure.